Insulation (pt 2) and plasterboarding

After an arduous weekend of unrelenting studio graft Sal and I completed the insulation and added plasterboard over the top in preparation for the arrival of the electrician.

Putting the insulation in between the battens continued to be a lengthy process but, given that the walls are free-standing, I’d be uncomfortable with larger gaps between the battens (600mm). In the end the insulation has probably taken the best part of 20 hours to cut, fit, and cover in foil tape. On the subject of foil tape we used almost 300 metres of the stuff (6 rolls) – about 50% of the time was putting this up rather than the insulation itself.

Doing the plasterboarding was relatively straightforward but definitely a case of ‘measure twice and cut once’. I made sure to mark the cable runs on the front of the boards so I didn’t accidentally put a screw through a cable when fixing up the plasterboard and, after a miserable experience with the first board, I made a note of where the battens ran behind the boards so I could draw a line to follow when screwing the boards to the battens from the front.

The hole you can see in the last  picture is a space for a plywood panel to use as a backboard for the TV mount. If I thought about it I’d have put the sockets on the right and the AV sockets on the left as I could then have dropped the cables straight down rather than the awkward 90 degree bend I’m going to have to put in, however this is a small point and I’m sure I’ll live.

No costs this time as the previous post covered them.

Next up: Justin the electrician brings the power!

Lessons

  • As per the previous post be really accurate with your battening. I mentioned that my innacurate measuring and placement of the battening hurt me on the insulation, it did so again on the plasterboarding and I had to cut every panel individually.
  • Take the time to mark the battens and cable runs on the front of each board, it makes it much easier to put the boards up and add screws with confidence – I nearly hit a cable and it made me very sad as I had to take a bunch of insulation our to check the cable.
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Wiring and Insulation (pt 1)

Having battened out the inside we’ve spent the last week and a half running the wiring around the studio and fitting the insulation into the framed walls. We have the electrician booked for a week today and, by that point, I need to have run the wiring, insulated, and put up all the plasterboard – busy!

Last week the electrician came round to validate the wiring I’ve already done in the garage and to talk through how I was intending to wire the studio. As we have to have a new consumer unit fitted to get power out there he’s pretty happy that there’s enough work for him to make it worth his while. The wiring basically consists of a new ring from the new consumer unit in the garage running round the studio and up over the door, the bottom of the sockets are 470mm from the floor except for the one up on the wall to power the tv (picture 1). Lighting-wise there’s an external dusk-dawn light and an internal, overhead, set of spots – the junction boxes for the switching are in the top of the wall next to the door (photos 2 and 7).

When it came to the insulation I used a fine tooth panel saw to cut the 50mm Xtratherm panels to size to fit into the gaps in the battening, and about 30 seconds into sawing I stopped and fetched a fine dust mask – it’s a messy business that generates a lot of dust. Once I’d filled out the voids in a section I ran over the joints with foil tape to seal it all up.

A couple of points worth noting:

  • Photos 4, 5, and 6 show how I was insulating around the sockets. I used a section of 25mm Xtratherm behind the sockets on top of the noggin with a notch cut through to feed the wire with another panel of 25mm Xtratherm on the front around the socket to pad it out. In this way (with the 35mm back boxes) the back box protrudes 10mm out from the insulation ready to have the plasterboard put round it.
  • The above socket insulation method will also (hopefully) prevent condensation forming on the back of the backboxes as they are likely to be the coldest part of the overall wall.

Though this was the design/plan I’m not that concerned about condensation in the wall. Why not I hear you ask? Well I’ll tell you…

To allow for the expansion and contraction in the external structure I built the internal wall standalone so that it wouldn’t be affected. As a result there isn’t actually a very good seal behind it and so moisture is never going to get trapped there as it can always get around the edges. I don’t know what impact this is going to have on the performance of the insulation (I hope not too significant) but it does make a bit of a mockery of [1] my use of the foil tape and [2] the foil backed plasterboard I’ve ordered for the walls. Oh well.

Costs

  • 50mm Xtratherm insulation (11$): £242.00
  • Foil backed plasterboard (14$): £140.00
  • Foil tape (4 rolls): £10.00
  • 5mm ply for flooring (4$): £20.00
  • Metal backboxes: £15.00
  • 2.5mm and 1.5mm twin+earth: £40.00

Lessons

  • If you’re intending to fit insulation between your framing make sure that you position the framing consistently and exactly. I allowed the framing to wander by a few mm here and there and, if I was insulating over the top, it wouldn’t be a problem however, in this case, it meant I needed to measure and cut each piece specifically – annoying.

Battening the inside

Having completed the outside of the studio we’ve turned our attention to making the inside into something that Sal might actually be able to use to work in – step 1: batten out the inside ready for electrics and insulation.

When planning this work one of the key considerations was the expansion and contraction of the outside structure – log cabin buildings aren’t dimensionally stable and expand and contract with heat and moisture. We wanted to ensure that, once built, we’d be able to finish to a good standard and it would stay that way. In an attempt to achieve this the wall battening was laid out in the following way.

  1. First I placed a number of treated 19mm * 38mm battens horizontally on the wall. This way they would move as the outside wall expanded and contracted vertically (the expected direction of movement). This provided an air void between the external structure and the next layer to allow air to circulate and prevent condensation.
  2. Over this I placed a layer of breathable membrane and sealed it all up with waterproof tape. The purpose of the membrane is to prevent water vapour from reaching the insualtion should any water make it through the external structure. As the membrane is slightly stretchy it should remain intact as the structure expands and contracts.
  3. Finally I build the internal battening to hold the insulation and electrics out of 38mm * 63mm CLS timber. The internal walls were built freestanding, fixed only to the floor, to allow the external structure to move past them in expansion and contraction. A 25mm gap was left between the wall and ceiling to allow for this movement – I’ll cover this in some way once I’ve fininshed the walls and ceiling.

And that’s it – pretty straightforward all things considered.

Costs

  • External battening (19*38 treated): £40.00
  • Internal battening (38*63 cls): £170.00
  • Breathable membrane: £75.00
  • Screws and Nails: £15.00

Lessons

  • I don’t think I put up quite enough external battening and, as a result, the air gap is likely to be compromised. In hindsight I should have gone with 400mm centres all the way up the wall, this would also have made fitting the membrane that much easier.
  • And on that note I’m not sure how effective the membrane is going to be. Due to the construction of the ceiling in particular I had to make a lot of cuts and use a lot of tape. I’m pretty sure this means that the overall membrane envelope will be badly compromised so I’m not sure it was worth it.
  • Buy an electric mitre saw. I didn’t, and I spent a lot of time and energy with a handsaw and regretted it. It’s not impossible to do without but I wish I’d bought one at the outset.

Finishing the exterior

Having built the main shell we decided to fit the doors and windows and finish the exterior before cracking on with the internals – particularly as the weather seemed to be holding in some sort of fashion… and here the pain began.

The structure of the building is designed to slot together. Within the design the window frame is shipped as one piece and the door frame as 3 components (top, left, and right) that fit together for the doors to be hung off. Having hung the doors and have the door frame slip and change shape twice I took the radical step of taking a saw to the door frame and throwing it into the wood pile. I then replaced it with a single frame and sawed the doors down to fit – if you look closely you can see the change in door size from photo 1 to photo 2. Frankly this was the most depressing exercise as it resulted in me throwing away something that I’d paid for – never good.

Next we fitted some extra boards to the outside of the base of the studio. The purpose of these was [1] to make it look more attractive and tidy, [2] to prevent rain driving underneath and [3] to stop animals from making it their home. Ventilation has been provided in the boards to the rear to stop damp setting in.

I replaced the facia boards supplied with the kit with some larger, more substantial items made from treated boards. Primarily this was an aethetic choice however they also protect the end grain of the roof joists and the electrical/cable access on the garage end of the studio.

Finally I build some custom gutter boards and fittings so I can add gutters once I’ve sited the water butt(s). As with the door frame the design of the kit seems a little mysterious here as they clearly haven’t considered how the water will disperse from the roof.

So there it is, the finished exterior. To be honest there are parts that have been a real pain but, overall, I’m pretty pleased with how it looks.

Costs:

  • Wood for the above: £50.00-ish

Lessons for the future:

  • If something looks suspect (such as the door frame) it probably is. Address it at the time as it’ll be twice as much effort later.
  • I wish I’d fitted the roof shingles after the end facia boards – I’d have got a much tighter and probably more weatherproof result if I had.

Studio arrival and shell construction

Some three weeks after ordering the studio arrived and was deposited on the drive by Garden Buildings Direct. Inspecting the parts revealed a couple of breakages, one of which I couldn’t live with, so I requested a replacement which duely arrived. This process was pretty straight-forward and, whilst I didn’t feel embraced by the warmth of their exquisite customer service, they were easy to contact and answered all my questions quickly with only slight confusion. A solid ‘B’ grade.

Before assembly I covered every part in either Wickes Garden Colour paint (Herb Garden) or Wickes wood preservative to ensure that any water that did creep in wouldn’t cause issues. The painting/treating took 3 solid days to complete and was a logistical nightmare as we had to protect the parts from the inevitable rain – you can see the ranks of painted components in the garage in the photos above. Painting T&G is also fiddly hence the length of time it took.

Once a sunny day, and parental-shaped help, materialised we set out to build the structure itself. The first change/addition we made was to raise the studio up on an additional set of treated bearers and place damp-proof course on top of these before putting down the floor bearers from the studio kit. The purpose here was twofold:

  • To provide an additional airgap and ventilation underneath the floor insulation to prevent damp forming there.
  • To enable us, if the worst happens and a floor bearer begins to rot, to jack up the studio and replace it.

The studio itself went together quickly and easily and was built and roofed within 24 hours. Along the way we made two other additions that are worth noting:

  1. The second-to-last wall board finished very untidily with a free ‘tongue’ and a space to the underside of the roof. I cut a piece of infill from the broken part for which I’d received a replacement however it’s worth noting as, without this, I’d have an irritatingly poor finish here.
  2. The instructions said to screw the roof into the top of the walls to anchor them however the jointing here wasn’t very close and would have resulted in a slightly curved roof. We added an extra piece of 75mm * 50mm screwed to the top/outside of the wall to bridge the gap and provide a more solid base for the edge of the roof.

The roof was covered in underlay (heavily overlapped due to the shallow pitch of the roof) and then Wickes felt roofing shingles. both of which were relatively easy to work with. Internally we inserted 25mm foil-backed PIR between the floor joists and then boarded over. We would have liked 50mm insulation in the floor but we couldn’t fit it in due to the depth of the floor bearers.

Next job is to make it watertight. Good luck all!

Costs: £2810.00 total

  • Studio: £2200.00
  • Additional bearers, all plates, and DPC: £80.00
  • Wickes Garden Colour (4 tins) and preservative (1 Tin): £90.00
  • Polyester underlay (3 rolls) and Roof shingles (9 packs): £370.00
  • 4 sheets of 25mm foil-backed PIR: £40.00
  • Misc screws/nails/fixings: £30.00

Lessons:

  • Allow time in your schedule for the replacement of broken or warped parts – I had this experience and seemingly so does everyone else who orders one of these log cabin structures. I had to accept that there was a level of warping and breakage that I’d just have to live with.
  • Get the supplier to send you some offcuts to use as blocks for tapping the boards down and filling in gaps/tidying up. The tongue and groove style of the boards means that you can easily damage the tongue if tapping them and the shape is a swine to replicate when you’re trying to get a good finish.

Laying the Base

Having selected the location for the studio and the log cabin that we would use as the basic structure we set about laying the base. Laying the base itself was actually broken into three separate phases; laying the concrete slab, infill and paths, and steps and brickwork.

Laying the concrete slab

For the slab itself we went with 100mm of compacted hardcore under 100mm (ish) of concrete including a damp-proof membrane under the slab on sand blinding. The membrane is probably overkill but the cost of building it in was relatively trivial as I was providing the faff and labour – this is probably not the case if you’re having someone do it for you.

As I haven’t laid concrete before I played things a bit too safe and made the slab 100mm larger in both dimensions than the base of the studio – in hindsight this was an error and could allow water to catch on the edge of the slab and run underneath. Much better to be a bit more brave and make the slab the right size.

In terms of pouring the slab we calculated that we’d need about 1.2 cubic metres of concrete – rather than mix this ourselves by hand we brought in readymix from a company called Easymix. They mix the concrete on site so you get decent control over how wet you want the mix and they can tweak it as they go.

Infill and Paths

In an attempt to mitigate the issue I created by sizing the slab larger than the studio when I laid the path and infill between the main slab and the garage I did 2 things:

  1. I laid it 10mm lower than the main slab so that there was no danger of water running up and onto the slab in heavy rain.
  2. I created a slope away from the main slab on all the concrete and paths to keep them nice and clear.

With the laying of the concrete around the slab being very fiddly and less volume I didn’t go for readymix this time but hired a concrete mixer and bought the materials. Another point worth noting if your planning this kind of thing yourself is, though it’s not readily apparent from the pictures below, I was very careful about depths and heights of concrete. As a result the path matches height with the grass so I can run a mower over the edge – it’s a small point but it makes me happy.

Steps and Brickwork

And finally to tidy up I added a couple of steps and some brickwork to hide the exposed earth and concrete behind the garage capping the wall off with some old roofing tiles. Here I just mixed the limited amout of concrete required by hand.

Costs for laying the base:

Concrete slab £440.00

  • 3 bulk bags of hardcore: £105.00
  • Hire of whacker plate: £25.00
  • 1 bulk bag of sand: £45.00
  • Damp proof membrane: £15.00
  • Wood for shuttering/tamps etc: £40.00
  • Readymix: £210.00

Infill and Paths £89.00

  • Bulk bag of ballast: £40.00
  • 10 bags of ce ment (offer): £19.00
  • Hire of concrete mixer: £30.00
  • Wood for shuttering/tamps etc: £0.00 (re-used)

Steps and Brickwork £74.00

  • Ballast: £0.00 (used surplus)
  • Cement: £0.00 (used surplus)
  • 6 25kg bags building sand: £14.00
  • 150 cheap garden bricks: £60.00
  • Wood for shuttering/tamps etc: £0.00 (re-used)

Hints and Tips:

  • Lay the base exactly the size of the building you’re putting on it. It will look tidier and prevent any issues you might have with water running underneath.
  • When pouring the readymix we had 2 of us running barrows and tamping… 2 people is not enough. Ideally we’d have had 2 running barrows and another 2 doing the levelling and tamping – it made for a very hard hours work.

Making a Plan

Having selected the site and cleared it the time had come to actually choose what the heck to build. The removal of the old shed gave us an area of roughtly 2.5m * 4.5m for the studio so we hatched our plan. Basically this amounted to:

  • The building: In the end we plumped for a 4.5m Devon from Garden Buildings Direct in 35mm timber (for strength) with 19mm floor and roof (for strength) and double glazed windows (for warmth). Cost for this without roofing was £2200.00. There were several candidates we could have gone for but this had the right arrangement of doors and windows in the right positions.
  • The base: In addition to the base we also need some paths and, because the top of the garden is on a slope, there would also be some brickwork required to build a low wall. As a result we chose a plain old concrete slab for the base working on 100mm of concrete on 100mm of hardcore.
  • External finishing: The plan here was to use ‘shed paint’ for the main structure but to use underlay and felt shingles for the roof rather than roofing felt. Whilst this finish is relatively expensive (£400.00 rather than £150.00) we chose the felt shingles for aesthetic reasons – both our house and garage have red clay tiles on the roof and we wanted to, at least, attempt to do something roughly in this style.
  • Internal finishing: Internally the structure would be battened out with breathable membrane andthen 50mm foil-backed PIR board used for floor/wall/ceiling insulation. Vapour-shield plasterboard would cover this to add a moisture barrier. Essential services (electricity, TV, networking) would be provided.
  • Misc: As a result of a conversation with our friendly electrician we decided to add a new consumer unit to the garage and to replace the garage wiring and lighting as well as doing the studio – this decision was mainly taken when, after a bit of investigation, it became apparent that the garage sockets and lights were running on a spur from the extractor fan in the bathroom.

Working on this basis we worked out our schedule and costs. We didn’t have a firm budget in mind provided it came in at less than the ~£8000.00 estimated by the builders so we were pretty pleased when we ended up at £5500.00 including the site clearance.

Let’s remember that number and see how we do….