andyscotland

Should have been clearer it's an existing, relatively new, dryer and only building a small utility extension and converting the garage so MHVR not really worthwhile. Definitely something I'd consider for a new build.

Hi, In my new utility, I need to duct the tumble dryer to the outside. Unfortunately the layout means the duct needs to drop down and then across the wall behind the stacked dryer / washing machine. I want to minimise the depth to keep the appliances as close to the wall as possible. The total length of duct will be about 2.5m, with one 90 degree bend and potentially a pair of 45s to stagger the pipe away from the wall a bit once it gets past the appliances. I see Manrose do a tumble dryer kit with 110 x 54 duct. However AFAICS that only gives 5940mm2 - about 25% smaller than the 7854mm2 of the 100mm round dryer outlet. I'm wondering if that's only OK for the short 300mm run they supply with the kit, but undersized for my purposes? Would I be safer to use the 204 x 60 duct to get 12240mm2? I also looked at the 25 x 225 extra-low-profile ducting, which only gives 5625mm2 - it would be great to use something that thin if I could get away with it, but I was a bit concerned such a narrow duct could trap lint / fluff quite easily....

This might not work depending on your reveal /opening detail but could you make the opening a bit wider with a thin vertical cupboard either side of the frame for the curtains to recess into? Or similarly, recess a box into the floor for a blind roller? You could have a flap (maybe a nice timber board) that hinged toward the door, so when the curtains are open you don't see anything, and when the curtains/blinds are closed the flap is behind them. For floor to ceiling blinds you'd either need to have vertical wires for them to run up, or come up with some sort of telescopic support from the floor a bit like a marketing "popup" would have.

Excellent ?

I think also some have a waterless trap with a self-sealing membrane so that might not be 100% conclusive?

Just that's the manufacturer's spec for butt joints (which this will obv be) Thanks - given @Onoff comment too I'll have a think what I could glue on - maybe even include a thin bit of polystyrene/scrap insulation or something as a compressible layer. Also it's unlikely there'll be anyone but me walking on the roof in the foreseeable future so can probably get away without capping it at least at first.

@scottishjohn yes planning to laminate the whole thing in a single operation. Just wasn't sure if the hips needed treating differently from any other butt joint. Obviously would be easiest to just bandage over if that's sufficiently robust.

@Onoff I would love to, would have made a bunch of stuff easier internally. Unfortunately the existing wall is hard up to the boundary already ?

@Russell griffiths that's good to know - I'll maybe rebate it in then.

@Russell griffithsthanks - been trying to get an answer from the manufacturer for a week or so but not had much luck so far. Is your roof quite flat? I've seen that detail (routing out for the edge trim to sit flat) but had thought my roof is steep enough it wouldn't matter.

@Onoff aha, that makes sense. We're using 25x50 for battens - I'm very tight on space - which I think might be a bit wobbly to build on the ground. But I might still do the top/bottom runners continuous and routed like yours. I will stick to the plan of getting the floor insulation and chipboard down at roughly the same stage!

@onoff - looks great! I like the routed out detail on the top of the bottom batten. We fixed vertical battens and then top/middle/bottom noggins but I suspect it would have been much quicker to get the centres / plumb (and possibly more sturdy) doing it your way. There's still a couple of walls to do, and the battens inside the insulation for the service void - might try your technique for the next ones. Is that proplex / correx type board on top of the floor PIR in your batten pics? I've been trying to get my head round a bit of an upcoming sequencing / materials-double-handling issue, would be easier if I could get the floor PIR down now but leave the chipboard till later but I've been concerned about walking / working over it too much and damaging it.

@scottishjohn @Russell griffiths sorry - I've maybe not explained it very clearly. I've attached a drawing from the original 1980s garage plans - best image I have that shows the roof shape. The slightly unusual rafters have been altered / sistered a bit now as part of the conversion, and there's insulation going on top, but the basic shape is staying the same. I'm happy with the abutment to the house - the roof butts up to the brick walls, below the soffit overhang. I'll put wall fillet / simulated lead flashing there (although by the time the roof is built up, the section along the side of the house will be quite close to the soffit - so I'll probably enclose that area anyway since it will otherwise be very awkward to paint / maintain that bit of the soffit in future). The hip joins I'm asking about are the two diagonal ridges, running up to the house from the left / right corners of the wall facing you in the isometric. The original roof was corrugated sheeting with flat ridge pieces over that join. Does that make more sense what I'm asking?

@Onoff there should be an embarrassed laugh / face palm emoji

Will soon be ready to start on our GRP roof, have two queries about detailing that I'm struggling to find answers to. First, it's actually a low pitch (10ish degrees) L-shaped hipped roof on three planes. I'm not sure what to do at the three (gentle) ridge junctions. I don't otherwise need an expansion joint, and I don't really fancy the look of the "rolled" ridge/expansion joint trims sticking up. Can I just put flat trim over it? Or just bandage it as if it was any other butt joint? Second, I'm building rooflight kerbs on top. The sides will be faced in GRP with trim at the top up into the rooflight flashing. Do these need wall fillet / angle trims at the bottom where they meet the roof deck, or again can they just be bandaged and laminated over?

@Onoff yeah I thought that this afternoon but I think it probably is prohibitively expensive for this application. And overkill really, doesn't need much by way of weatherproofing.

@Ferdinand thanks - good point re shrinkage. By flexible foam do you mean pre-formed strip/roll rather than expanding foam? E.g. brickfill or similar, compressed into the joint so it will expand to fill any gap that appears over time? Re letting it shrink before install - what sort of timeframe is that? I've had the insulation on site a few months (made sense to order the same time as some other materials) so will potentially have already shrunk a bit but guessing may have more to go.

@Onoff @nod thanks, that's basically exactly what I had in mind before I started second guessing myself. Really helpful reassurance. Only slight difference is the wall battens are on DPC strips and the floor DPM taken up the front of them. That way if (despite the healthy condensation analysis) there did end up being any moisture on the inside of the blockwork it will run/drip down behind the DPM onto the garage slab.

Thanks, in my case the PIR on top of the old garage slab goes wall to wall, so the bottom end of the wall insulation would meet the foil face of that. The floor insulation is on a DPM so there should be quite a low risk of sucking up moisture? I know the skirting will cover the visible plasterboard gap, but it won't resolve the thermal bridge/bypass if there's an air gap? (although the inside end of that will be covered by the VCL).

For example, where the insulation on my warm lean-to roof butts up to the house brickwork? Or where the internal wall insulation (on battens on converted garage wall) meets the insulation on the top of the slab? I have seen Ecotherm's instructions for lining a room with insulated PB on battens say to cut it 10mm less than the height but I'm wondering if that's just to do with the plasterboard / ease of fitting. I know if e.g. between studs you'd just cut the PIR to fit tight. I had been thinking of cutting the boards very slightly short and then running a bead of expanding insulation foam to fill any gaps, but now am wondering if that's correct. I know thermally it wants to be continuous, so if I do need to leave a gap presumably I want to fill that with ...something... as an air gap would defeat the purpose?

As far as I know, the build cost for the warrant application is supposed to include a proper value for labour even if you're going to DIY/call in favours/whatever. Although it doesn't have to include the value of work not strictly relevant to the warrant (internal finishes etc) but there's very limited guidance on what exactly should/shouldn't be included. So I suspect a lot of people's figures are pretty notional. It does seem a fairly unreliable way of valuing/costing the work involved - if you specify £10k of high performance windows rather than £2k of cheap PVC that doesn't really make any difference to the council checking they meet the appropriate BS/u-values/whatever...

Thanks - yes, u values and fire are all ok and it's a warm roof.

A warm roof has the vapour control and insulation on top, hard up against the covering. So the rafters etc are "warm" as they're inside the heated space. A cold roof has the insulation between/below rafters and requires ventilation below the roof covering to prevent condensation.

I did a full plans submission, but the (approved) spec just says the GRP system and substrate needs to meet fire rating AC or better. I didn't mention a particular manufacturer or anything more specific, though there is a general line at the beginning that all works and materials to comply with relevant BS and EN standards. So I could assume that if they wanted to require BBA that would have been flagged already - but just a little cautious as my council (who will be inspecting) are known for being stricter than the council they subcontracted my warrant application to.

Thanks all, helpful comments. It's only a fairly small area (30sqm) relative to the rest of the house and we do not expect to sell. It's a warm roof, and actually low pitched rather than flat (around 8 - 10 degrees) so no issues with fall. Unfortunately building control have to date refused to engage with the project at all - don't want to hear from me until I'm ready for completion certificate and on a couple of things I've attempted to confirm their approval of ahead of time they won't say any more than it's for me to ensure that I can demonstrate at completion it complies with the regs.... I guess basically I just want reassurance that if I put a non-BBA-but-fire-certified product on there the building control inspector won't make me replace it at completion...