Build an Addition Onto Your House!

Ever wanted more space in your house? Are you unhappy with the current layout of your home? Well then it seems like you might need to build an addition onto it! When I bought my house it had a pretty crappy single bedroom addition that was not properly sealed to the ground and was oddly laid out on a lower level than the rest of my house. I wanted more square footage and wanted to really learn how to build house stuff so I figured I should build an addition myself! I had previously built a shed/workshop in my backyard and figured it wouldn't be too hard... I estimated I could knock out an addition in about 6 months working full time on it. A year tops if it went a lot slower than I was expecting... Overall my addition ended up taking the large portion of two and a half years.

I'm definitely not an expert at anything building related but with an electrical engineering background, experience building some sheds and a bunch of woodworking projects I figured I could figure it out. It was a lot harder and took way longer than I initially thought it was going to. I ended up making out pretty well on it financially but it is definitely the thing I've worked the hardest on in my entire life so far. This instructable is not going to walk through every single step of the build but rather provide a general overview of the process I went through to build my addition. After reading through this instructable hopefully you have a general idea of where to start your research/planning/studying so that you can build some cool stuff onto your houses! Just about every step of this instructable has multiple different books written on it, dedicated professionals who whole job it is to do it and multiple youtube channels dedicated to them. I try to link to resources I found to be helpful during each step. Hopefully by reading this instructable you can get a better general idea of the steps you need to follow and the resources to learn from to build something awesome!

The time lapse of the whole addition build might be one of the coolest things I've ever made. A longer 6 minute version of it is on youtube here if you want to see the full house renovation/addition build I did in more detail! I used a gopro powered by an external USB battery pack to capture a picture every ten seconds and then used iMovie and later Adobe premiere pro to stitch it into a video. It mostly worked pretty well... There are only a couple of gaps and jumps in progress from it deciding to not record properly that day. Based on the 10 seconds a frame the time lapse covers around 2,000 hours of work in either a minute or six minutes depending on which one you are watching!

Now let's start with looking at some of the tools that you will need to build an addition!

Note: Be sure to take on any building project at your own risk and comply with any and all local building codes/permits/laws when attempting to build anything. Don't hurt yourself and don't build anything that will hurt someone else.

If you decide to build your own addition hopefully you live close to a hardware store. I just pulled up my mint account and found the number of transactions I made at Home Depot over the duration of the addition build and I went 371 times over 2.5 years. I also had some Lowes and different woodworking store trips so overall I had 468 home improvement transactions over 2.5 years which averaged out to 468 trips / 912.5 days so about a trip to a hardware store every 2 days. Sometimes this would be 2 or 3 trips to different stores trying to find a part or picking up stuff I forgot in one day and some online transactions but overall you are going to need to get very familiar with your local hardware store.

One of the most useful things that will help you build an addition is a trailer or some way to transport a bunch of stuff. I picked up my 4x8 utility trailer Daenerys Towgerian (who gets pulled around by my jeep wrangler Khal Wrango :) ) when I first bought my house and it by far was the single most useful thing I've bought.

In addition to the trailer having a shed/woodshop stocked with a bandsaw, tablesaw and a ton of different hand tools also came in quite handy but was not totally necessary. I'm working on another instructable on the build of this shed/shop and I'll link to that here when I finish it up!

Overall though these tools are pretty indispensable and you should almost definitely pick them up if you are going to try to build an addition onto your house:

• A good set of battery operated portable tools. Definitely including a circular saw, drill, impact driver, oscillating cutter, sawzall and spare batteries. I started with a cheap set of Ryobi tools and they were pretty good but batteries wore out pretty quickly. I then went with the pricier Milwaukee 18V line. When I was buying them they had the best battery packs on the market and they have worked pretty well for me so far so I'd probably recommend them. Go with whatever brand you like or whatever mix of brands you prefer but going cordless is a huge improvement to running electrical cords all over.
• A good compressor and air hoses. I went with a California Air Systems one that has worked pretty flawlessly for me so far! It is definitely not quiet when it kicks on though.
• Basically like all of the nail guns they sell. You pretty quickly will accumulate a bunch of nail guns. I think I have seven? Eight maybe? I lost count... A framing, roofing and trim nail gun will cover you for most stuff though.
• A ladder and fall protection system. Gotta make sure you can reach your roof/siding and if you happen to fall it hopefully it wont hurt too badly...
• Proper PPE including gloves, ear protection, eye protection and respirators. Building is dangerous. Demolition is dangerous. Make sure you have a good first aid kit handy in case you get injured and make sure to properly understand the dangers you are exposing yourself to.
• A bunch of other hand tools and power tools. A good laser level, tape measure, hammer, utility knife, miter saw and concrete mixer helped me out a ton on this build.

You will need a lot of tools to build an addition and having the right ones really does help a ton. Make friends with the employees at your local hardware store and find somewhere to rent the bigger tools that you might only use once but will save you hours of work. I rented a drywall lift and sander, an excavator, a trencher, a jackhammer, and flooring nailer for my addition. Make sure you do your research and shop around before you jump into buying or renting anything so that you know what you are getting into! If you can find someone to help you build your addition that will probably be one of the most key things you can do. If you have two people the struggle of getting heavy things into place and the general flow of work will more than double. If it is just you working on it your productivity and the tool on your body will slow you down way more than if you are working with someone else! Now that you have a general idea of the tools that you need for your addition lets get into what it takes to plan out the build and get it permitted.

One of the most important steps of a major building project on your house is making sure that you are legally allowed to build it. I built my addition under a subject to field inspection permit which meant I had to do a lot less paperwork than a fully documented/architect designed/engineer approved addition. Depending on where you live the rules for subject to field inspection permits and what you need to supply to get one approved and what you are allowed to build with this permit vary greatly. My house was in Seattle and the King County Construction and Inspection department publishes a bunch of tip sheets that help you through the process of getting a permit. I used the ones on getting a permit, subject to field inspection permits and site plan requirements the most. Reach out to your local building department and talk to them about what you are planning and get their guidance on it. Reading a bunch of house building books also helps! I thought these ones were quite useful: Renovation 5th Edition, Room Additions, Building Additions. If you don't want to try and design your own addition this would be a great time to hire and start working with an architect. If you are trying something really ambitious or working in a treacherous area you should probably get an architect/structural engineer to develop your addition plans.

I had to go into the permitting office I think like five times before my plans were finally approved. My house was a 660 sq ft two bedroom one bath house with the crappy addition when I bought it. I started by drawing up a floor plan in sketchup of the current layout and then modifying that until I got something that I was happy with and looked doable. I initially sketched out ending up with a three bedroom two bath house and it looked pretty good as a floor plan. I then modeled it is a rough 3D model to try and figure out how I was going to actually build it. I would have needed to tear off my entire roof and this would have meant relocating my main electrical drop and it not being able to be covered by a STFI permit so I ended up scrapping this idea and going with extending the roof line as close as I could to my shed and adding a bigger bedroom and bathroom on the same level. I had to add a bunch of details to my site plan and a bunch of figures showing how I was actually going to build this addition after talking to the permitting office and after adding in everything they wanted I got the approval to start working on my addition! This started with getting rid of the existing crappy addition I already had in my house...

If you don't have a crappy addition built on your house already this step might just be tearing some siding off of your house but either way you need to get your existing house ready for your new addition. This is probably one of the more dangerous steps so make sure you are being careful and properly using your PPE. My buddy Matt (thanks again for the help Matt!) helped me with this step and we almost got stung by wasps that were hiding under my siding so watch out for critters that might be hiding. Also key is to either re-route or remove any live electrical wires that are in the area that you are working on. This might require a different permit from your local government so make sure to get that permit and do all your work to code!

It is hard to describe the feeling of taking a sawzall to the walls of your house and then pushing them over. It is very weirdly awesome and really highlights how insubstantial most modern houses are... But regardless of how awesome demolition is make sure to take it slow and start from the top, work your way down and try to salvage as much as possible from your demolition. Making sure that the pieces fit in your truck or trailer is also quite helpful. Once you have your crappy addition demolished it is time to start working on the foundation of your new addition!

A house is only as strong as its foundation so make sure you don't mess up this step for your addition. This step could look very different for you depending on what your plans call out but since my addition was quite large I ended up having to pour a very substantial foundation. My approved plans called out a neatly dug, rebar reinforced stem wall running around the outside of my addition and a 6x6 beam supported by concrete piers down the center of it. This ended up being 6.84 tons of concrete that me and a couple of friends poured by hand. If I was to do this over I definitely would have hired a company to come and pour/pump the concrete from a truck rather than doing this by hand. I initially thought it wasn't going to be too bad to do by the bag but bags of concrete are really really heavy and you get really really tired carrying them around. Thank you so much to all of the friends and family that helped me pour this! Maureen, Ben, Sai, Mia, Christine and Ilan I'm eternally grateful for your help with pouring this foundation! Make sure that you add in proper drainage for your foundation so that any water is properly directed away from your house too!

Before pouring any concrete I had to move a bunch of dirt that was part of the hillside that my house was built on. I rented an excavator and trencher to help with this but mostly just moved it by hand with a shovel and wheelbarrow. The more that you can do with machinery the better. Your body will thank you.

After using the laser level to make sure I had moved enough dirt I then started neatly digging the trench for the bottom of the stem wall. My plans called out a stem wall that is in an upside down T shape with rebar reinforcing running the full length of it. Make sure to check with your local inspecting agency to ensure that your foundation is properly built and reinforced. A rebar bender was really helpful for this step since anytime I had rebar going up one of the steps or turning a corner I had to bend a piece of rebar and tie it on so that I had the proper overlap between the pieces. The little plastic rebar chairs and pre cut steel rebar ties are also super helpful for this step. The basic steps I followed were to neatly dig a trench for the top of the upside down T part of the stem wall, add in the rebar (including the vertical ones that tie the T together), get it inspected, pour the top of the T for each of the steps, add the reinforcing rebar and build forms for the rest of the T, get it inspected again, pour the rest of the T and then before the concrete dries embedded a bunch of J bolts into it so that you can tie your sill plate 2x4's to them properly. After all of this you can then hopefully get your foundation signed off as ready to go by your inspector! I really should have built sturdier forms for the second part of the pour since it ended up bowing out and almost failing in a couple of places. Buying and installing some of these snap off concrete form ties would probably have been a pretty good idea. Luckily my stem wall wasn't very tall and it it bowing didn't really affect the rest of the build.

After getting my main stem wall foundation poured I had to add in a center support so my floor joists didn't span too long of a distance. I accomplished this by digging some pier foundation support holes, pouring a bunch of concrete into them and then embedding a 6x6 bracket into them. I then got a bunch of 6x6's, the appropriate post cap brackets and fasteners and built a pretty giant balance beam through the middle of my addition! Once you have this step done you can start framing in a giant dance floor...

After you have your foundation and balance beam installed and signed off on by your inspector you can start framing out the floor of your addition. Make sure to use a joist span calculator and check with your local building department to make sure that the planned size and spacing of your floor joists is up to code! I eded up with 2x8 joists spaced every 16" on center and they ended up being about 11.5' in length. With the middle balance beam support they only spanned like 5.25' so the floor was quite sturdy! Any lumber that you have directly in contact your poured concrete foundation needs to be treated lumber or have at least a plastic barrier between it and the concrete. Any nails you use in the bottom layer of framing also need to be galvanized so that moisture build up on the concrete doesn't eventually corrode them. The treated 2x4's are then tied down onto the stem wall by the 1/2" J bolts that were embedded into the concrete and are then secured down by giant earthquake proof square washers and galvanized bolts. After the stem wall is then extended up to the proper height needed by additional untreated 2x4 framing the floor joists can start to be installed. Make sure to use properly sized framing nails when you are building up your stem wall and framing out the floor. I went with this framing nailer and it has worked pretty excellently.

I started framing out the floor by laying out a couple of 12' long 2x8's that would make up the outside perimeter of the addition. I then cut my 2x8 joists to fit inside of this perimeter and nailed them in place through the outer board. For where I didn't have easy access to the other side of the board to nail through cause my existing house was in the way I used metal joist hangers and a nail gun designed to nail them into place with the proper structurally rated nails. I then added in solid blocking to tie each of the joists together and continued down until I reached the end of the planned addition. At this point you need to get your floor framing signed off by the inspector and if it passes you can start covering it or fix any of the issues that they identify.

After all of the floor joists were installed and I passed my framing inspection I then laid down my sub floor. I went with 3/4" thick tongue and groove plywood. I used construction adhesive along the floor joists and nailed them down so that I ideally wouldn't have a squeaky subfloor. Using a scrap piece of wood and a sledge hammer helps to snug up the tongue and groove joints too. I installed them oversize and then trimmed them flush with a flush trim bit installed in my router. You can pretty easily trim them to size with a circular saw too though. Now that the dance floor is installed its time to give your addition some walls!

After the floor of your addition is roughed in then it is time to start building your walls! The books I mentioned above (Renovation 5th Edition, Room Additions, Building Additions) all give a lot of great examples of how to frame in different features and how to lay out your framing properly. In general though marking your top and bottom plates before you start nailing is always a good practice. Adding most of your sheathing before standing your walls up is quite helpful too as long as you are able to still stand up the heavier walls. Make sure everything is level and square before adding in your double top plates since anything being out of plumb now will make the next steps way more difficult!

On the longer wall of my addition I had to frame it out in two sections since I wasn't able to stand it up in one giant section. This introduced a slight bow in the framing that was quite annoying to work around and I really should have worked harder to fix it in this step since it made the rafters not fit properly and just looks bad. Make sure that your framing is as level and plumb as possible and your future self will thank you! Once you have your walls all framed out and you pass their framing inspection it is time to start working on your roof!

Once you have your walls stood up it is time to get a roof over it so that all of your hard work so far doesn't get ruined by the rain! My plans called for 2x6 rafters that were at around a 30 degree angle that matched the existing roof line and just extended further out to cover the new addition. I thought a miter saw would be really useful to cut these angles really precisely and repeatably but getting the long 2x6's positioned on the saw ended up being quite annoying. I made a jig out of scrap wood that would guide my circular saw to the correct angle and then used a jigsaw to cut out the birds-mouth notch on the bottom edge of the rafter so that it would sit on the top of the framed in walls. Once I had one rafter cut I could trace out the lines to cut and use the circular saw jig to batch out a bunch of them. I then also cut a 2x6 to fit across the whole length of the addition that I butted up against and nailed to the roof rafters to act as the ceiling joist. For the overhangs I cut 2x6 rafters without the birds-mouth and then used some 2x6 blocks to bump my roof out the desired foot and then screwed through the outer rafter into the blocking from both sides. Current building code requires metal hurricane ties to make sure your roof doesn't blow off in heavy wind so once those were installed on all of my rafters I could start on the decking of roof!

I went with plywood roof decking to give it a bit more strength compared to OSB but either would have probably worked fine. I used my framing nailer to install the sheets of plywood onto the new rafters. I then installed my facia boards, metal drip edge and synthetic shingle underlayment paper. I decided to go with a ridge vent along the full length of my addition and so I used a circular saw to cut that vent opening in before installing the rolls of it and starting to shingle it. A roofing nail gun also comes in super handy for this step! I installed the roof over the majority of my addition first, covered the rest of it with some tarps, finished a bunch more of the stuff I needed to do for the rest of the house renovation and then came back and then later tore off the rest of my old roof shingles and re-roofed my whole house. Anytime you are on your roof make sure your ladders are set up securely and that you are properly using a fall protection harness. If you can have your shingles delivered to your roof top that will also save you a ton of work carrying them up a ladder. After your roof is on, it passes it's inspection and everything is being properly kept dry now it is time to work on the sides of your addition!

Now that your roof is on it is time to finish up the rest of the outside work by adding some some siding to your addition! I initially placed a large order for a bunch of the lumber and materials that I estimated that I would need for my addition/house remodel and in this order I decided on siding my house with cedar shingles. This single decision easily added like eight months of work to this project. Had I decided to go with any other siding type it would have been way easier and quicker. It totally makes sense to me why cedar shingles fell out widespread use as a siding but they did end up looking pretty awesome! I'm in the process of writing a separate instructable detailing what I learned installing these shingles and some of the tricks I developed to help install them. I'll link that here when I finish it up!

Regardless of which siding type you pick you will want to install your house wrap over your sheathing as soon as your inspector passes your sheathing/framing inspection so you can protect it from the rain. I taped all of the building paper edges with tyvek house wrap tape and used 1/2 in staples to attach it to the sheathing. I then used self adhering window flashing and silicone caulking to really ensure that my windows were sealed in properly and then screwed their flanges in.

At this stage I also installed a continuous vent on all of my eaves so that I would get good airflow into my attic up through the eaves and out the ridge vent. This was quite annoying to instal and I should probably have gone with a bunch of individual vents that I think would have been easier to install. I sprayed all of my eaves white with a paint sprayer before I installed any siding so I wouldn't have to worry about getting any drips or overspray on my new siding.

Once your windows are all sealed up properly and your eaves are installed and painted you can get to siding your addition! This step was extremely tedious and pretty dangerous since it was like all on a ladder and the cedar shingles were super annoying to install. This is probably something that I would hire out on any of my next builds. After everything is sided its time to start working on the inside of your new addition!

Once you've finished up all of the outside work on your addition you can move on to starting work on the inside! One of the first inside things I did was get started on the electrical work. Just about any and all electrical work will need a separate electrical permit pulled so make sure you get all of your work permitted and that you know how to safely perform the work. If this isn't the case then hire an electrician for this step! I'm an electrical engineer and had done a decent amount of home wiring stuff before tackling this project so I decided to attempt it myself. The rest of my home renovation involved replacing my main breaker box, installing solar panels, running power out to my shed and installing an EV charger so the couple of outlets, switches and lights in the addition was quite easy compared to all of that stuff! Helpful books for household wiring are: Wiring a House, and Code for Homeowners.

After you get a permit for your planned electrical work the next step is to rough it in. This means installing the outlet boxes, switch boxes and planned ceiling boxes and running wiring to them. Installing permanently wired in smoke detectors and AFCI breakers for your new wiring is I think code in most of the country now and is a good idea regardless of whether or not it is required by your local code. Once it is roughed in you can get your rough in inspection of it done. The inspector will either have pickups for you or give you permission to proceed onto the next steps of your build. For my rough in the inspector made sure that I had nail plates properly installed anywhere where my wiring was close to the face of the stud and that I had sealed with spray foam anywhere the wires penetrated the top or bottom plates of my framing. After the rough in you can then cover it with insulation/drywall and then you just need to get in inspected for a final inspection after all of your outlets/switches and fixtures are installed.

For my addition I was adding in a full bathroom so I had to add the plumbing for a sink, toilet and bathtub. This was my first major plumbing project and overall it was pretty confusing but went pretty smoothly. If you don't want to learn a bunch about pipes and fitting this also something that is also quite easy to hire out. If you do plan on doing it yourself talking to your inspector and sending them a planned sketch of everything you plan to do is quite helpful and lets you get their feedback before you spend a bunch of time installing pipes that you need to tear out if you mess it up. These books were quite helpful for giving a general idea of what you need to do for most plumbing projects: Plumbing and Renovation 5th Edition. Similar to electrical wiring once you get a bunch of you pipes installed you need to get a plumbing rough in inspection done. One of the things pointed out to me before my rough in inspection was that I needed to install a back flow valve in my main drain line since my fixtures were at risk of backing up if the sewer line in the street backed up since I was below the level of the next upstream manhole cover. After getting this installed I could then start working on the new addition plumbing.

For all of my new plumbing I sketched out what I planned to do then got feedback from my inspector on my plan. Laying out the planned fittings and taking a picture of them helped me illustrate and communicate what I was planning. All of my new addition plumbing was added into the my main waste stack with a 3" ABS waste Wye connection. Immediately after this I added a 3" ABS test fitting from Holdrite. With this 3" test fitting installed I could isolate my new plumbing from my existing plumbing and continue to use the rest of the plumbing in my house as I worked on the new stuff. This test fitting also lets you perform a water test on your drainage piping by connecting a garden hose to it and filling it up to the vent on your roof with water. You then wait a bit and make sure the water level didn't drop to make sure you don't have any leaks in it. After getting an ok on my plan I then ran all of the ABS drain pipes to their proper location and then plugged them with properly sized test plugs so that I could pass my water test. After running a bunch of new PEX supplies lines I was then ready to get my plumbing rough in inspection done! I luckily passed and didn't have to tear out any of my newly installed plumbing! After getting the ok to cover my plumbing I could then install my insulation.

Insulating was a pretty easy step since if you spaced your framing out its just a matter of stapling up some properly sized batts of insulation but you could also hire this out and have people spray insulation for a bit more R factor for this step. I added a bit of spray foam behind my outlet boxes where I couldn't really fit any insulation but other than that this was pretty straightforward. Make sure to not have any of your plumbing in exterior walls so that you don't have frozen pipes and make sure to insulate all of your exterior walls! After passing your insulation inspection you should be ready to cover everything with drywall!

After you have all of your utilities roughed in and your insulation installed its time to start hanging some drywall! I rented a drywall lift for this step and it ended up helping a ton. In general you want to try to minimize the number of seams you have in your drywall and make sure they are properly secured with enough drywall screws. This book was quite helpful for giving you a good breakdown of the whole drywalling process: Drywall Book. Cutting out outlet holes and switch boxes was quite annoying but a drywall rotary cutter helps to make this process go a lot quicker. For my addition it worked out that a full sheet fit horizontally against the top of my walls, a full sheet fit horizontally along the bottom and then I had a like four inch strip that I could fill in with off cuts at an easy working height of four feet up.

After all of the sheets were hung you then go through and apply joint compound to all of the seams, corners and screw holes, add a layer of tape on the seams and corners and then a final coat of joint compound. I sorta sucked at this step and ended up applying my joint compound too heavily so that I had to sand it down a ton after it dried and had a decent amount of cracking that I had to then fill in with more compound. This ended up taking a lot longer than it probably should have but eventually I got pretty decent results. I rented a drywall sander that helped a ton and would highly recommend getting one if you have to sand a bunch of drywall.

Once the joint compound is dried and looking pretty good I decided to add some texture to my walls so that the spots where I messed up a bit wouldn't be too noticeable. This big drywall texture hopper was good for doing large areas and this smaller spray texture gun was good for touchups and small areas since it was a lot easier to set up and had very little clean up associated with it. After everything is nice and textured it is time to get everything painted and install some flooring!

Painting is one of my least favorite parts of any project and this was no exception. After I installed and caulked a bunch of window trim and then taped off anything that I didn't want to get covered in paint I used my paint sprayer to get everything painted pretty quickly! Make sure to wear a face shield and respirator for this step so you aren't breathing in any tiny drops of paint! I applied two coats and that seemed to be good enough for me.

After your paint is nice and dry you can start installing your flooring! I went with hardwood hickory in my hallway and main bedroom of my addition and hexagonal tile sheets in the bathroom. At this point I think I also installed the tub and shower surround since I needed to tile up to the tub and needed to make sure that was installed before I started tiling. I rented a flooring nailer and used it to install the hardwood floor. To tile my bathroom I first laid down a layer of general purpose thinset compound, screwed down backer boards, taped and added compound to the seams, added down a layer of thinset troweled with the proper sized trowel for my tile and then laid down the sheets of the tile. I then waited for that to set up and came back through and applied a dark black grout to fill in the spaces between the tiles. There are a bunch of really good flooring tutorials on youtube so be sure to check them out and get a good set of kneepads since you will be on your knees a bunch while you install them. Once everything is painted and flooring is installed your addition really starts to look like a finished room and theres just a couple of things left to wrap up on it!

Once you have everything painted and your floors installed it is time to install all of your plumbing fixtures, electrical fixtures, outlets and switches. Reading the instructions that come with all of the stuff you decide on installing and googling install videos should hopefully answer any questions you have on them. Once you get your final inspection you are then free to enjoy your new addition! Soon after finishing my addition I sold my house and so I was able to get some fancy pictures of the finished project once it was nicely staged and looked way nicer than the entire time that I was living in it. It was just a bit of an improvement from when I first bought my house and it was in really really rough shape!

I'm entering this instructable into the home improvement contest so if you enjoyed it please vote for it to win! If you have any questions feel free to leave them in the comments or message me and I'll try my best to get an answer for you!