Garden Room - Workshop

The background to this project is that my daughter was having her home remodelled and the ‘old’ (about 10 years old) UPVC doors and windows were to be discarded. They could have perhaps been sold on eBay but as they would be collection only, this would limit the market somewhat. The builders where quite happy to put them all in the waste skip. I was toying with the idea of building a garden room to use as my stained glass workshop. My present workshop was the house garage and the natural light is quite poor for my hobby. Also everything gets covered in wood dust whenever I do a carpentry project. These double glazed units seemed ideal as the basis of a light and airy workshop/garden room.

Obviously the Legacy door and window frames would dictate the size and format of the finished building and would need to be designed around regarding their size and format.

I used Visio as a scale design tool. I input all the existing UPVC frame sizes and then played about with possible variations. I wanted to abut the building onto an existing party wall and not protrude too far into the garden. As there was an existing path (although not very good!) I took this as the extremity of the building width. I roughly judged the length to fit in with an existing garden shed and another old path 90degrees to the first one. Unfortunately I couldn’t make the height as low I would have liked as the door frames are full size suited to a main dwelling. This meant the base would need to be of minimal depth  and the roof pitch also kept to the minimal. I had hoped for a greenhouse style pitched roof but this would result in the final building being way too tall. I made some wooden scale models once I had decided the final format to show my neighbours so that they could have some input if they wanted to.

Some other Structural considerations were that I didn’t want the building to overhang my neighbours wall or to lean against it or hang on it. Garden walls aren’t particularly strong structurally and ours was over 100 years old. I also wanted to be able to gather rainwater from it to use in my veg garden. After weeks of planning and deliberation I came up with the offset ridge design. Not as easy to build as first envisaged but it ticked all the boxes.

After clearing the site of approximately 2 tonnes of topsoil and levelling it up, I used one tonne of crushed stone as hardcore which I whacked down. I utilised the topsoil in raised beds for growing vegetables. The trees and bushes were extremely hard to dig out and I bought a Matock which was invaluable for this grueling task. Fortunately my son Mark came from Australia to visit and offered to help with the hard graft of laying the pavers. Also my next door neighbour very kindly brought the pavers from my daughters house in his shiny new 4x4 vehicle. Without this really great practical help I would probably still be staring at the wild garden and dreaming of building the workshop! Thanks guys! (and my beautiful daughter for giving me all the materials. On top of the compacted hardcore we laid 50-60mm of sand and cement mixed dryish. 4:1 ratio, then watered it well once the last paving stone was laid. The pavers are heavy duty 50mm. we were two short so we left two spaces and in-filled the void with mixer cleanings, spare stone and 3:1 ratio sand and cement. I needed to be careful to protect the existing mains and water services pipes and cables when laying this base. I buried them and covered them with plastic guttering to allow expansion and stop the concrete gripping them.

Frames:

I decided on a Modular build consisting of two sides and one front one front. This way I can build each frame and then store it until they’re all done and then assemble them. By building in the existing UPVC frames at each stage I can ensure they’re fixed firmly and squarely.

 The timber type I used was fairly low quality softwood suitable for studding or internal framing. I bought a good quality wood preservative and pre–treated all the cut lengths before fixing. I used a nail gun to attach timber to timber and high quality woodscrews to attach the UPVC frames to the wooden structure.

First Frame Design

After the base was hard enough to stand on, I used it as a working area to construct the front frame. I laid it out by cutting the top and bottom beams first, knowing they’re length was the same as the base. I had made several small models to help me visualise the best layout of the UPVC frames that I had inherited.  I clamped the UPVC frame to the top and bottom beams to determine the exact length of the upright frame beams. Once measured I cut four of these. I could then lay out the door and window frames to see what looked right. After playing about for a bit I decided to have the long window at the same height as the door on narrow frames. I also decided to have two uprights frame beams at each corner for strength and to accommodate the exterior cladding. After a bit more thought it seemed right to add another upright to each of the other vertical members too.

This allows for the 4x2 s to be attached snugly at each corner by offering a 4” connection. It also allows for the mid ones to accommodate equal amounts of external cladding. I need to make each double vertical beam the same width, which is an equal amount that is left when subtracting the three UPVC frames then divided by four. All the off-cuts can be utilised in the framework beneath the long window. I will try to make them spaced right to allow for the internal insulation board to just fit in. After some thought I decided to dispense with the door sills and the window sills. I don’t think it will compromise the weatherproof factor, especially if good amounts of quality sealant are used. As it turned out the front elevation was protected from the weather by the roof overhang.

First Frame construction

The next stage involves treating all the frame pieces with wood preservative then nailing them from top and bottom with pneumatic ring nails. The door and window frames will be attached with high quality wood screws from the UPVC side into the wooden framework. All the door and window frames will be located flush with the front face of the wooden frame.

I decided to build the front frame on a trellis stage so that I wasn’t knelt down building it. Using several clamps I was able to hold everything in register whilst fixing each part. The long window was the first to be located in the upper right hand of the front frame. At each fixing I checked the square before nailing or screwing. I decided to use double frame uprights between each of the UPVC frames. I calculated the gap by moving all the elements to the left hand side of the bottom beam and measuring the remaining space. I then divided the 100mm by the four uprights and thus needed to have a 25mm gap. I found a suitable piece of timber and used this for a spacer when building the frame.

Because I used low grade timber a lot of it was twisted slightly so I had to choose each piece carefully, often having to substitute pieces as I went along. Once I had cut the pieces I treated them with a high quality wood preservative. To make sure all the uprights were the same length I ganged them together and sanded them all to the same length.

Two days work resulted in the front frame completed. A few mistakes where nearly made. The doors would have been opening inwards which wouldn’t have worked. Luckily I had photos from the original building that these UPVC units had been removed from and could refer to these. The finished front frame needed extra hands to move it from the trellis once completed.

End frame Design

The end frames need careful thought, one to allow the rear guttering to be accommodated and two to make sure the abutting wall doesn’t take any stress. Its only a garden wall and not built for load bearing. By making sure that the new building is constructed in a stand-alone way and only abutting the wall not using if for strength it should retain integrity. In all elements of designing this build I am trying to consider my neighbours perspective and make sure that there is minimal impact visually and structurally. I’ve considered several ways to build the small rear facing roof section. The most difficult elements to consider with the side frames are the fact that the UPVC frames are taller than the dividing garden wall that the building will stand next to. To this end I have used two different roof angles and lengths. With the rear facing roof section being shingled it will not overlook or shed light onto the neighbouring property. Making the guttering lower than the adjoining wall, whilst retaining waterproof properties also raised many challenges. Once the ridge timber, guttering parts and facia board had been delivered I could use these to estimate the angles needed to accommodate the rear roof design. The main upright struts look like they need to be about 25 degrees and this would allow the ridge beam to sit on top of the wooden frames holding the UPVC door frames. This should make the front roof fall at about 2-3 degrees. A full size mock up is still needed to confirm these first guess calculations.

The key here is to assembly everything absolutley square and level. I was out by 30mm on 2.4m and I had to make painful modifications when I tried to attach the roof panels some weeks later, that are exactly 90 degrees square. I should have checked diagonals to ensure 100% square build, which I didn’t do and paid for it later on. <beware!>

I first started by hanging the DPC sheet onto the garden wall, then as I joined the frames together and these stood against the DPC I could ensure all would be dry in the garden room. I decided to use a very strong ridge beam and hang everything off this. I ended up with a front roof fall angle of about 4 degrees. The polycarbonate roof sheet manufactuers say that 5 degrees is the minimum fall. The small rear roof is about 60 degrees and felted. I installed a plastic guttering and then felted it again into the gulley, using eaves protection sheets for good measure. Due to the difference between the polycarbonate roof sheets and the base size I ended up with a front roof overhang. This looked ok so I decided to leave the roof sheets intact and went for the overhang. The side frame design allowed for the rear gulley to be below the adjoining wall yet accommodate the full size UPVC frames.

The final completion is fairly straightforward and the pictures tell the story best. I attached the outside cladding with staples and this was a very quick and easy method. The roof panels came with alloy glazing sections and I finished the roof off with sticky lead glazing tape.

Colour choice and paint type. I matched the exterior colour to my existing garden shed and the paint is actually masonry paint but its very easy to apply and is durable. The upvc painting was difficult and it had to be keyed in with fine abrasive pads and a special Upvc primer applied before painting with the green masonry paint. time will tell if its durable or not. For the Internal cladding I used 12mm water resistant MDF with rock wool insulation between the frames. I did the electric first fix before the cladding. I tried to  maintain the integrity of the DPC membrane at all times.

The floor construction was 18 mm waterproof plywood and also got the same DPC and insulation, again taking care not to pierce the DPC. Finally I re-glazed the UPVC frames (they where too heavy to manage with the glass in place. Two panels had been broken by the builders when removed from their original location. I couldn’t afford new double glazed units at £80 each so I bought two one inch thick polycarbonate sheets at £16 each. Most of the cost of this build was in the roof sheets, the carpet and the blinds. I added some privacy film and a fly screen I had spare. I battered up the base edges with a stiff mix of sharp sand and cement pulling both the dpc’s together, the one on the base and the one on behind the external cladding. This looks as if it will maintain the water barrier at the foot of the building ok – time will tell.

There was a few problems with the rainwater pipes as they’re not meant to run horizontally but I sorted them out with duct tape and silicone sealer. I led them in together so that I can eventually collect all the rainwater in a tub for garden use. The front rainwater gulley needed a bit of fiddling with to get it snug but it ended up ok. The front facia and soffit boards where the off cuts of the 18mm floor plywood. I trimmed everything with some hardwood 'L' section that I acquired a few years ago.

I butchered up an old oak desk that I had bought years ago for a fiver, and with two Ikea worktops I cobbled together a bespoke working area for my stained glass. I attached the tops with hinges at the front edge so that they can be tilted up to work on, if needed. I plan to make a raising mechanism with an old car scissor jack eventually. The place has had a few torrential rain tests and so far it seems watertight. It gets very hot though, when the sun is fully on the front windows but that’s not all bad. My wife has commandeered one end as a clothes drying area, so everyone’s happy. Especial thanks to my lovely wife who painted the entire building over several very hot summer days! she also helped me at several difficult stages over the full build. Thanks babe! x