Clad to meet you

 We had a ready supply of featherboard from deconstructing the old fence around the site, so we decided to recycle this as cladding.

This turned out to be one of the most time-consuming bits of the build, as each board needed sanding to remove any lichen and algae, treating with fire retardant, and finally painting. It saved us a fair bit of money though, even with the eye-watering cost of the fire retardant.

The finished boards were cut to length and screwed to the battens, with a couple of trim pieces at each corner to finish things off.

The next stage of the project will involve sorting out the access, fitting a water butt and some solar power too.

Windows and roof

With the weather getting worse, it was becoming annoyingly urgent to get the build finished. The next big task was to fit our box-section metal roof. This arrived ready cut to length , but some lucky person still had to get on the roof and fix it down. That turned out to be muggins.

We went with a "warm roof" design which more or less mirrored the construction of our walls, only with roof sheets instead of cladding. The sheets were fixed on with self-tapping screws which have a little neoprene washer to stop water getting under them.

Roof done and it was time to fit the door and windows. This turned out to be surprisingly hard. The main problem is that there doesn't seem to be a lot of information out there on how to fit windows in timber-framed buildings - all the DIY guides assume you're building in brick, which to be fair is the default for the UK. Even the ultra-detailed Irish Vernacular website (which gives step-by step instructions on how to build a small timber-framed family home) just says "see elsewhere for window details"


The windows themselves were pretty easy to install (it's simple to pop out the glass from most UPVC windows, which then lets you screw the window frame to the wall timbers).

The silver stuff round the windows in the picture above is bitumen-backed flashing tape, which we put round the edges of the window frames prior to fitting the windows. In hindsight this was a mistake, as it made our windows an extremely tight fit, and didn't really contribute to weatherproofing as water can just get down the sides of the window frame.We also found that you can't use silicone sealant with bitumen products, but luckily there's a product called "roofer's sealant" that does work, so we used this to close up any gaps at the edge of the window frames.

We fixed our window trims to the edge of the frame, but spaced them out slightly so they covered the join between the window and the wall.

The top bit of trim was fitted at a slight downwards angle to let water drain off it, and covered with flashing tape.

Tools

You could build a project like this using just hand tools if you wanted, but power tools were a massive time saver. 

A decent cordless drill was the tool we used the most, not for drilling but for putting the frame together. We used 60mm timber screws, which have a star head instead of the usual Posidrive or Phillips, and they worked amazingly well. Also, lithium ion batteries rock. They weigh less than the old style NiCad ones and charge super quickly, so you don't have to down tools for the day because of a flat battery.

A circular saw was also essential for cutting sheet materials quickly, as well as for fiddly jobs like profiling the edges of windowsills.

A chop saw made cutting up the timber to make the frame very easy indeed. We actually got given this one, I'm assuming because its size makes storage somewhat challenging.

We also splashed out on a power planer, which turned out to be useful for skimming off wood round window frames, making wonky cuts straighter, and general bodging.

Building, part 2

After an amazing fun day building the frame, with loads of help from our friends, the next bit of the build was frustrating and a bit rushed, as we struggled to get a skin on the building before the weather turned bad. Sheathing board is very soft and malleable, and our stuff was also tongue and groove fitting, so there were plenty of frustrating moments as we tried to fit a bashed tongue into a dented groove without snapping the board, or our patience. We were able to cover the roof from the inside in one very long evening's work.

Those metal posts were part of the fence around the substation, and we started with some vague idea of keeping them, but later gave up and chopped them off with an angle grinder. It was very noisy and fun.

We still had to fit the outside rails to the roof, which meant tangling with the undergrowth.

By this point it was really starting to look like a building. Not very weatherproof at the front though.

 With some help from Jerome and Dee we fitted a waterproof breather membrane, which should stop any rain from getting into the actual shell of the building. There are different grades of this material. Some types are designed to replace roofing felt and hardly breathe at all, and some are designed to allow water vapour to escape, just like your fancy Gore-Tex jacket.

We didn't realise this and ended up having to return some, as it would have made our walls about as breathable as a carrier bag. There needs to be some way for water vapour to escape from every building without condensing inside it (or worse, inside the walls) and it took some head scratching to work out what order things went together in. The order we decided on was, from inside to out, plywood > insulation/wall timber > sheathing board > breather membrane > battens > wood cladding. If we got this wrong, please don't tell us.

At this stage we still hadn't ordered the roof due to dithering over what colour to get, so we decided to start lining the building. First the insulation went in.

The slabs of insulation fitted into the walls snugly, but the ceiling was more problematic due to gravity's influence and the slightly erratic spacing of our joists. As a temporary fix, we cut some long ribbons of spare breather membrane and used them to hold the insulation in place until we came to screw the boards over it.

The next stage was fitting the plywood boards that lined the structure. After a while it was hard to stop seeing faces in these.

One thing about using ply: it's quite hard to cut large sheets of material accurately enough to avoid gaps between them. And now I can also understand why things like skirting boards exist.

Building

Building started, logically enough, with the floor. We put the frame together in two halves which we man (and woman) handled into position on the concrete blobs. Unlike the walls, the floor needs to support the weight of people walking on it, so although it was all built from 55 x 100mm timber we used joist hangers (which required some bodging as most hangers are designed for 150 mm timber).

The frame was beefed up with some noggings and then we lifted the whole thing up (just about manageable with two of us), chocked it with some wood, and attached breather membrane to the underside. This was a bit fiddly, and I can now consider myself an expert at operating a staple gun at a funny angle.

The gaps in the floor were filled with insulation and the floor boards fixed on top. At this point we decided to go ahead and sand the floor before the walls were installed, as we wouldn't have to be as neat round the edges or worry about the mess.

The wall plates were assembled ready for some extra muscle to move them into position. The two longer walls were made in two parts so we could lift them, then connected in situ.

At this point we really needed a few extra bodies to get everything into position, so some friends were bribed with food and beer. Over the course of an afternoon we managed to get all the frame for the building into position and fixed together.The lintels for the door and windows were knocked into place once the frame was up, then the joists went on.

 As the walls went up, they were skinned with sheathing board to add rigidity and some weather proofing. We had already had one minor disaster when rain got into the floor plate and soaked some of the insulation, which meant we had to stop work, dismantle the floor and dry out the damp bits before reassembling. With the walls now resting on the floor, we wouldn't be able to do this, so it became even more important to get it weatherproofed.

Preparation

Before starting work on the build there was a fair bit of work to do on the site. The substation had sat in the middle of two trenches containing coolant, and by the time we got hold of the site they had been filled up with mud, sand and assorted rubbish, including two mature willow trees. Rather than building on top of a midden, we decided to clear out the trenches and remove any organic matter and growing things that could make life difficult for us in the future.

With the rubbish and spoil from the trenches bagged up and taken to the tip, the next stage was to get the site ready for building the floor. The concrete base wasn't quite level, made worse by the fact that it had cracked in places, so we mixed up some more concrete and dabbed around 20 small blobs at regular intervals to support our floor plate. Time to start building!

The ingredients

The great thing about designing your own building is that you can start rounding up materials before you have any idea what it's going to look like. The first thing we got was some reclaimed timber, previously the seating of a local bar, until they decided to rip it all out and replace it. Some of this later turned into work benches.

Windows and doors are parts of a build that have the potential to get very spendy, very quickly. Having obtained a quote for a set of bifold doors that was nearly as much as we were planning to spend on the entire build, we started scouring classifieds websites for something a bit more careworn and affordable. An advert in Gumtree led us to a massive set of sliding patio doors. Yes, they had glazing too. The cost was a couple of hundred quid, compared to £500 for a new set, and £1,000 or more for bifolds.

On to the windows. You can actually buy custom-made double glazing units fairly cheaply, but we wanted to do this even cheaper if possible. A local reclamation yard provided two double glazed windows in the same "trouser press brown" finish. No idea what the U-value of these is, and they've seen better days, but they're still a vast improvement on the single glazed windows that feature on the bigger sizes of garden shed.

For the timber frame, we decided to use standard construction timber (or "carcassing" to give its thrash metal-tastic alternative name). This comes in standard sizes, including 44x100mm and 44x150mm. In proper houses, 100mm is usually reserved for non-load bearing walls, but we decided to use it for the walls and floor, to make the frame easier to handle and keep the overall height of the structure low. An initial plan to use 100mm timber for the roof was quickly beefed up to 150mm after Celia's dad made some remarks about the unsupported span, and reminded us that we'd probably need to clamber about on it to fit the roofing.

This building is going to be used all year round, so some insulation is a must. Quite a lot of insulation in fact, given its size. For value and thermal performance Celotex board is hard to beat, but it's messy to cut to size, and has that landfill-in-waiting feel about it. It felt right to blow some of the money we were saving elsewhere on some insulation with good performance and green credentials. so we want for Steicoflex insulation, which is made from recycled wood fibre and is nicer to handle than fiberglass, performs better than wool, and will hopefully return to the earth with good grace one day, instead of hanging around forever. It's available in standard widths to suit various joist spacings.

We decided to sheath the outside of our frame with insulating board, which reduces heat transfer through the timber structure, stiffens up the frame, and also acts as a temporary weatherproof skin for the building until the waterproof membrane and cladding are added. Also, if you're a cat, it's great for sharpening your claws on.

For the lining of the interior of the building we chose plywood, taking the cheap and cheerful option at our local DIY megashed. With hindsight I wish we'd gone for proper wall cladding material, or at least better quality ply. The price was right, but the amount of warped and damaged pieces became very tiresome later on. We used OSB (the board that looks like a thin sheet of Weetabix) for the floor, with the idea of sanding and varnishing this later.

We didn't decide on roofing or cladding material until after the build had started. For the roof, we wanted something that would work at a shallow pitch, and be removable if we ever dismantled the room. The angle of the roof ruled out rustic materials like shingles, and I didn't like the idea of having to replace a huge expanse of felt every few years, so in the end we went with box profile sheet metal.

We were told by our local supplier to pick a light colour, because otherwise the room would quickly become unbearably hot in the sunshine. However some quick research revealed that if you've got a decent amount of insulation, the colour of your roof becomes much less important. We ended up going with a dark graphite colour to make the building blend in a bit.

For the exterior cladding of the walls, we had a big supply of featherboard from the fence around the site. These weren't in the best condition but we sanded them up and treated them with a fantastically expensive fire proofing solution (you're supposed to build the exterior walls of outbuildings near property boundaries from "substantially non-combustible materials", which seems like common sense if you're constructing a large wooden box) before applying a wax-rich grey paint.

With these materials rounded up, the next stage was to finish preparing the site.