Garden Office
You can find information and images below detailing the complete construction of my garden office. I required additional space for a small office and server room set-up for my business, and the only place to expand to at the time was the garden. It's been repurposed since then, but that's covered in another project article.
Step 1 - Design + Clearing the area
The first thing I did was research into the various different ways that I could build the office, for the lowest possible cost (actually the first thing I did was check to see if it would be cheaper having a HIAB drop a shipping container which I could then convert, but meh...). The question was then whether it would be easier to pour a concrete foundation (I recall at the time weighing up a raft foundation using rebar) and build it from block, or whether I could just simply concrete in block pad stones and build a timber frame on top of that. My primary concern with a timber frame was that insulating and cladding it would push the material cost higher then if I simply used block, however I found a great way to keep the cladding cost down (more on that later), and so opted for the timber frame. I then did a quick bit of cost-benefit analysis into using SIP's (structural insulated panel's) instead of a standard timber construction. Just looking at my old spreadsheet, the quote I got at the time was almost double what it would cost in timber and insulation, so obviously I went with the timber construction. The rest of the materials were fairly easy to determine; corrugated bitumen sheets for the roof, p5 t&g chipboard sheets for the floor and plasterboard sheets for the internal wall. There are a few more core materials that I'll cover later.
I had to remove a couple of tree stumps, but the farm jack made light work of them.
Step 2 - Preparing the site + foundations
The area designated for the office was sloped, and so the ground had to be dug down and a small retaining wall erected. The easiest way to accomplish this was to dig a narrow trench and install paving slabs vertically within the trench. They were then concreted in place, backfilled with soil, and further paving slabs placed on top to finish. With this complete, I then measured and dug out the trench holes where the foundation blocks would be installed and concreted into place. I had to ensure these were plumb and level, so quite a lot of time was spent on this task. I could have installed wood shims on the timber base frame later to make it level, however I would have then been exposing cut timber which would rot over time. The timber base frame doesn't sit directly on the blocks; there is a layer of damp protection to ensure that no damp travels between the ground and the timber base frame.
Notice the two washing lines attached to concrete blobs? They were a pain to remove...
Step 3 - Base and wall construction
Skipping forward a bit here, the floor frame is constructed, and the t&g floor boards screwed into place. The stud walls are then each constructed and raised into place, where they were temporarily held in place with wooden braces. Apart from one wall (the one shown in the image), I had to raise and nail all the walls into place myself, so this task was a bit tricky.
Things are finally starting to take shape!
Step 4 - Door frame + double top plate
In order to create the required fall for the roof, the front wall of the structure is constructed taller. The front wall also has the door framing built in prior to being erected, and is built with a king stud to help provide additional support for the door frame. The top plate is then installed to provide additional roof support. I probably could have managed without the king stud, and maybe even without the top plate, however when I was calculating the measurements the additional cost and work involved was negligible, and considering the total weight of the building I didn't fancy compromising on building standards for the sake of a few quid, only for it later to fall down on my head.
Floor and timber studwork completed
Step 5 - Roof rafters and vapour permeable membrane
The roof rafters were then lifted and nailed into place. The roof overhangs the front and the rear, to provide enough space for the necessary ventilation to occur. In order to prevent the roof from sweating, a 50mm air passage exists within the rafters, between the roof insulation and the roofing sheets (technical note: it's referred to as a cold roof). Vapour permeable membrane is then applied to the outside layer of structure. This is part of a series of layers that are designed to prevent interstitial condensation forming within the structure - more on this shortly.
Roof rafters on and vapour permeable membrane applied
Step 6 - Plastic cladding + roof sheets + trim
This is skipping forward a bit, but it's easier to do it in this order since it's the last series of actions to occur to the external structure. I mentioned at the start that I figured out a way to clad the building on the cheap, and the answer to this comes in the form of soffit boards. They're intended to be installed on the underside of the eaves of a roof (and I do indeed use them for this too), however they work just as well as external wall cladding; at a fraction of the cost. The roof sheets are installed on top of roof battens that run across the length of the roof, and the trim and guttering is applied once it's all in place. Vents are then installed within the soffits at the front, and an air gap at the underside of the rear of the roof facilitates the necessary flow of air across the roof space. The door frame and door have also been hung at this point.
Jumping forward a bit here: roof, cladding, and trim installed
Step 7 - Insulation
The insulation is installed between the studs and roof rafters. I opted to use rockwool to save on costs, although the hassle in installing it meant that I regretted it shortly afterwards; installation within the walls was fine, but getting it to stay within the roof space was a major hassle. In the end I needed to create a web of string to temporarily suspend it in place. I then installed a layer of aluminium plastic to all the internal walls and ceiling. I forgot to get pictures of this, but basically the entire inside of the building was very VERY shiny. It was thankfully very easy to install; I simply stapled it into place, and sealed it with aluminium tape. I wasn't aiming for a hermetically sealed room as such, but the reduction in air flow between the internal and external space of the building was intended to help control the transfer of heat. Adding the additional internal barrier means that any change in temperature between the inside and outside of the building (specifically hot to cold) would create condensation on the cold side of wall (which in the UK is the outside). It was a bit of an experiment based on a lot of research I conducted at the time, however I've not had any issues with mold in the walls to-date, so it seems to have worked, even if only by chance!
Inside now, insulation installed between studwork.
Step 8 - Plasterboard + Electrics + Carpet
The plasterboard was fairly straightward to install, and to save on time and considerable effort I decided to just paint the plasterboard after screwing it into place and finishing the jointing. The finish was actually a lot better than I expected, but I figured that if it did look a bit shoddy I could have always wallpapered it later. The only thing I didn't do on this project was the electrical installation; mainly because I couldn't legally (Part P requirement), but also because (in my opinion) mains electricity isn't something that should be handled as a DIY'er. I opted for surface mounted sockets, simply to save on installation costs, but also to make the installation of additional sockets easier if I decide to do so in the future. I then installed the skirting board, and fitted a nice black office carpet. And that's pretty much it!
Internal aluminium sheet, followed by plasterboard, then electrics installed.