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79 lines
8.0 KiB
Plaintext
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title: "Floors and ceilings"
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---
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Work on the garden room continues. Since my last post, the floot and ceiling have been completed, and I've ordered the lime for the walls. Let's take a look.
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## Ceiling
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I tackled this first, which in retrospect was a mistake - since the floor is suspended, it would have involved less teetering on ladders if I'd done that first! Oh well.
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The overall buildup is a "cold roof", with the EPDM and OSB3 underlay separated from the insulation by a 50mm air gap. This is ventilated - the wind comes in at the eaves and blows along the rafters, from front to back, helping to dry out any condensation. Below that, I put 100mm of rockwool - taking me to level with the underside of the joists - held in place with 25x50mm battens, running along at 400mm centres. Covering all that, I put another 50mm of rockwool, and fixed it in place with resilient bars (for acoustic insulation) running crosswise to the battens, again at 400mm centres. Finally, I fixed some pine matchboard (tongue & groove, 12.5mm thickness) to the resilient bars. Phew. Some pics -
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=> /img/floors-and-ceilings/buildup.png Early attempt to model the buildup
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=> /img/floors-and-ceilings/rockwool-one.jpg First layer of rockwool, held up by battens
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=> /img/floors-and-ceilings/rockwool-two.jpg Second layer of rockwool, held up by resilient bars
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=> /img/floors-and-ceilings/matchboard-one.jpg Getting started with the matchboard for the ceiling
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=> /img/floors-and-ceilings/matchboard-two.jpg Finished ceiling
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Nothing's ever quite that simple, of course.
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Before I started, I decided to cover the inside face of the roofplate with "wood fibre board", as that's an airtightness detail. I ended up using cut-up loft boards, which are particle, rather than fibre, but they're *probably* fine for indoors.
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Since the rockwool was 600mm wide, I had to cut every piece going between the joists (400mm) to size. I was going for a fairly tight fit, again to help with airtightness, and achieved that - but it meant the pieces would often end up being higher than the bottom of the joists, so eating into the 50mm air gap. I spent a fair bit of time with bits of batten, poking at the rockwool from the external access to the cavity, to get it working.
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I'd not thought about supporting the edges of the battens that held up the first layer of rockwool; in the end I got a bunch of little metal angle brackets and used those. Awkward, though.
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The second layer of rockwool was 50mm going into a ~40mm space, so had to be compressed a bit, especially under the battens where the available space dropped to 15mm or so. That compromises the insulation value some, and was also fiddlier than expected.
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The matchboard was prone to splitting at the edges, getting the tongue & groove mated was a pain, and I had some finicky cuts to make at the front of the garden room. Lovely stuff though and it completely changed the way the room smells the moment it was in place.
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Even with all those issues sorted out, it was still a royal pain to get all the parts up and fixed. It would have been easier to put the battens in place then drop the insulation down from above, for instance. Got there in the end though, and it looks alright.
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I still need to put something up to hide the expansion gap between ceiling and wall; coving or something. I'll seal the void with something airtight and flexible, like butyl tape, before that goes up, and for simplicitly I'll be rendering to be flush with whatever depth it ends up being.
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## Floor
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The main issue with the floor was the joists - I was using a mix of C24 6x2, and C16 8x2, due to an ordering mix-up. They were attached to the box beam with joist hangers, and I was careful enough with their placement to get a surface that's within 0.1° of level, so that worked out well enough. However, the ground level was quite uneven and I needed to dig trenches to make room for several of them. My new SDS drill was very helpful for that!
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Once the joists were down, we friction fitted 150mm rockwool between the joists, then put (new) floorboards down on top of that. Much simpler than the ceiling buildup. I was originally planning to use some old decking boards that I'd saved from ripping it out last year, but in the end I wanted a better finish, a continuous wood surface (3.6M long boards) and a tongue&groove between boards for airtightness.
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More pics -
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=> /img/floors-and-ceilings/floor-one.jpg Joists in
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=> /img/floors-and-ceilings/floor-two.jpg Rockwool in
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=> /img/floors-and-ceilings/floor-three.jpg Boards going down
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=> /img/floors-and-ceilings/floor-four.jpg ~fin
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This ended up being much easier than the ceiling, and I'm much happier with the finish. Even the cuts for the front of the room are better, and everything is fixed down with hidden "tongue tight" screws, so it ends up being a continuous wooden surface.
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I'm debating removing the OSB at the door threshold and continuing the floorboards out; it would look better, but would also make them structural, so I'm unsure just now. There's a little gap to fill if I don't, which will be a pain to cut - but possible.
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As with the ceiling, also left to do is some skirting along the floor, covering the expansion gap. More butyl tape, and again, the plaster will end up being flush with it, so I'll render whatever the plane between skirting and coving ends up being, most likely. I'll be surprised if it's exactly vertical!
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## Tung oil
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The wood surfaces for floor and ceiling are untreated right now, and the floor at least definitely needs protection from traffic. I did a bit of research and decided "pure tung oil" was the way to go - this is a "drying" oil that polymerises on contact with air to form a hard, matte finish on the wood. In the pure form, i.e., with no thinners added, it's completely food-safe (although not very tasty) and doesn't emit anything nasty when it's drying or afterwards. Application is labour-intensive, though - you need several very thin coats, with at least a day between each. So far I've just practiced on a couple of offcuts, but it seems fine.
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I'll be getting on with the ceiling shortly; the floor will wait until after rendering is complete, as the finish will be ruined by that process otherwise.
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## Next
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Now it has a floor, we're already using it - but there's plenty more to do. I need to fit the windows, re-fit the doors (they're about 2° off level right now), and get the walls ready for rendering. Inside, that involves a lot of stuffing of gaps, trimming of surfaces, and digging out straw for niches, shelves, etc. Particularly around the southwest corner, there are some pretty large voids where bales don't meet properly - it's the corner where I learned how to do the 105° angle, and could be much better.
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Outside, it's mostly about getting a level surface by trimming away excess straw. In particular, I've got a few bales that stick out significantly past the line of the wall - I just need to be brave and cut away the excess, then re-tie the bale strings. I'm hopeful the compression on the wall will keep most of each bale in place as I do this, but who knows? I've never done it before. Exciting!
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Once the walls are prepped, I can actually do the rendering - 22M² indoors, and about the same outdoors (since the back wall doesn't need rendering outside). I phoned up the Lincolnshire Lime folk and had a very good chat; on the strength of that, I've got 500kg of St Astier NHL 3.5 being delivered next week, as 20x 25kg bags. It's a little stronger than is generally used for indoors, but should be fine, and it's a simplification to do inside and outside identically.
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=> https://www.lincolnshirelime.co.uk
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=> https://www.stastier.co.uk/lime/lc-pure-nhl-3-5/
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Cheap, and hopefully fairly foolproof - being hydraulic gives it a chemical set so the chances of it failing are much reduced. It needs less aftercare than a render based on regular lime putty, and makes for a much more durable surface. I've never done it before - only messed around with some clay plaster on the course - so I'll be learning on the job. Fortunately, I've got one external wall that's mostly out of sight to start on...
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