MortarThePoint

I was worried that it would affect the strength of the junction with the plasterboard stopping in free space rather than on a stud.

I could put 36mm x 4mm stripwood behind the OSB3 at all its studs to make it effectively 15mm:

The sketch above has the issue of the plasterboard needing to come away from the OCB towards the corner. Or am I better off creating a small pocket in the corner to get filled by plaster when the wet plastering is done? They may not look it, but the sketches are pretty much to scale.

I'm looking to include OSB in the Bathroom wall but it's complicated by there being a return. The wall sheathing will effectively be changing thickness at the return which is a small challenge. Also, I may only be able to get 11mm OSB (or 18mm but same problem) which means it's not the same as the 15mm plasterboard. Below is a drawing of what I'm looking at. The green is 15mm or 12.5mm moisture resistant plasterboard, yellow is 11mm OSB3 and grey is 15mm Duraline. All on 70mm C-Studs (BG) in blue.

The AAV could be above the sink and behind the mirror. To service the AAV, I could remove the mirror and an access panel. I suppose it raises the question of how does air enter the wall and does it bring moisture in with it? I know there are small trap based AAVs but suspect they wouldn't admit enough air to prevent the problem in this situation. 9l/s for 1¼" solvent weld pipe https://mcalpineplumbing.com/air-admittance-valves/ventapipe/vpsf-4050-ventapipe-4050

Thanks Nick. The bath is freestanding so it would be a pain to have an AAV there. Could the AAV be in the stud wall with some form of air access to the stud wall? Another option that might be possible is to keep the bath and basin wastes separate all the way to the stack. This is what I was worrying about in terms of an S-trap: Though it would be more like this I guess: Could I solve it all by having the AAV off that initial in wall elbow? If just having the AAV in the wall, I would make sure it is well above the top of the basin.

The pipe goes about 500mm along the floor, joins the bath waste and goes 200mm down through floor before going 1800mm along ceiling void and joining soil stack. I may not pass through floor though and join stack above floor, but that area will be very busy. So I can't going purely horizontally to the stack unless I penetrate the wall at skirting board level which would be strange.

The basin would have a U-trap before the wall penetration so combined with the 90degree in the wall that would make an S-trap. That's bad for symphonic emptying isn't it? What are you thoughts on height?

Hmm, does this second drawing create an S-trap which is a no-no?

What height should my waste pipe go into the stud wall? Exciting times getting the partitions up and starts to feel like a home. I want to route the waste pipe of a basin through the wall to have a clean finish in the bathroom. There's only one place I have to do this, others are on blockwork walls or behind cabinets. The wall is 70mm C-studs (BG) and I plan to use 32mm ABS solvent weld pipe. The main question I have is what height the pipe should penetrate the wall for attachment to the basin. The basin will be a free standing one (wooden unit with basin on top). We haven't chosen this item yet and it may be one I make myself, but it would be nice to have the pipe at a sensible height that allows options. I'll probably fit a pattress to allow the future option of hanging a basin on the wall, but haven't decided yet. The cut-outs of the studs are around 500mm off the bottom, though I think I can flip them over and make it more like 300mm. Should I do that and then have a vertical section on the right of the drawing as in the second image which allows easier future adjustment of the wall penetration? At the end of the wall there will then be a vertical to get down to a trench in the screed. I hope this isn't noisy. At the moment the floor channel of the stud wall is screwed to a 4x2 which is continuous to the wall so I'll have to work out how to butcher that to make the trench go under the floor channel. If I can't do that, I'd have to box in the pipe at floor level which would be unfortunate, but not the end of the world. The trench is about 500mm long before a large hole in the floor that will be shared with a bath waste. rodding access

A point worth knowing is that British Gypsum 70mm C-studs accommodate 32mm waste pipe through their cut-outs but Tradeline don't. Neither accommodate 40mm waste pipe. The cut-outs in 70mm Acoustic studs are way to small.

Here's a potential gotcha. For bathrooms, C-studs should be at 400mm c/c if using any 15mm Gyproc moisture resistant grade plasterboard. It doesn't actually say what stud c/c to use if using 12.5mm moisture resistant plasterboard. A Siniat video about metal stud partitions says they should be at 400mm c/c due to the extra weight of tiles.

I was finding it hard to find the British Gypsum Site Book and Good Practice Guide so thought I would upload it here for anyone else who wants it. British-Gypsum-Good-Practice-Guide.pdf

Forgot to do the division: dU = 4.167 * (0.025m *0.002m) * 60W/mk / 0.171m = 0.073W/m2K I've checked with Arthur Hough and there AH120 (aka GL6) is 0.8mm thick. BG suggest 600mm x 600mm centres (see extract below), reducing the number per square meter to 2.78/m2. That reduces the thermal bridging to dU = 2.78 * (0.025m *0.0008m) * 60W/mk / 0.171m = 0.020W/m2K. That first number seems so large (e.g. changing 0.15 to 0.22) that it can't be right. I guess it is treating it as a bridge all the way through to cold which isn't really fair. To do it properly needs FEA. Alternative model would be to consider GL6 in series with a block of wood to cold. the length of the block of wood would be the thickness of insulation remaining past the end of the connector, so 80mm in my case. What area to make the block of wood? 27x27 : r_wood = 0.080 / 0.12*0.027*0.027 = 914, r_gl6 = 143, r_total = 1067 --> dU = 2.78 / 1067 = 0.003 47x50 : r_wood = 0.080 / 0.12*0.047*0.050 = 284, r_gl6 = 143, r_total = 427 --> dU = 2.78 / 427 = 0.007 47x81 : r_wood = 0.080 / 0.12*0.047*0.081 = 175, r_gl6 = 143, r_total = 318 --> dU = 2.78 / 318 = 0.009 Feels reasonable to assume that the affect of using GL6 connectors vs some magic non-conductive ones is dU = 0.005 - 0.010, I'm happy to work with 0.005. Removing 50mm wide by insulation_thickness_below_rafters timber battens improves the U-value by dU = 0.004 so the GL6s cancel that out and it comes down purely to cost and ease of installation. Also putting it into context, it's all equivalent to a difference of about 7mm of Mineral Wool! I was uneasy that my pitched section's U-value was rounding up to 0.15 rather than down to 0.14. A single 1m2 window cancels out 120m2 of that difference!

You can use Resilient Bar on ceilings and on walls so it stands to reason (?) you can use them under the rafters of a pitched roof. I'm tossing up between the following three options, all to allow 75mm of below rafter Mineral Wool insulation: 50x47 timber batten on 25mm standoff blocks [£1.20/m] 50x25 timber battens on 50mm stand off blocks (strong enough to take my weight on a single one spanning 600mm) [£0.80/m) Resilient Bar on 63mm standoff blocks (no way strong enough for me to stand on) [£1.50/m for comparison as at 400mm c/c unlike timber at 600mm c/c] The Resilient Bar has the benefit of near eliminating the batten thermal bridge as the insulation behind it would be the full 75mm except where the blocks are which improves U-value by about 0.004. One thing I can't decide if it's a good thing or a bad thing is that Resilient Bar won't couple the plasterboard to the trusses as solidly as timber battens would. The bad side of that could be a sloped wall with a bit of give, though I haven't heard of people complaining about walls with Resilient Bar being flimsy, but maybe that's because of the sound isolation meaning I can't hear their cries. The good side is that it could protect the plasterboard from minor movements of the trusses as they age. Could that help avoid cracking. Obviously the Resilient Bar would be good for sound isolation, but that's not needed here. Has anyone used Resilient Bar under rafters or have any thoughts on this?

I saw some videos of a larger renovation in France in which they used the GL6 connectors. Well I've given myself a bit of a shock working out the thermal bridge of one of these GL6 connectors. Steel has a lambda value of around 60 W/mK whereas pine has a value of round 0.18W/mk. That's a factor of 333. If these are at 400mm c/c x 600mm c/c that works out as 4.167/m2. If the average equivalent width is 25mm (reduced from 27mm by the holes) and the thickness is 2mm (guessing, will check) then the loss per m2 would be 4.167 * (0.025m *0.002m) * 60W/mk / 0.171m = 0.0125W/m2K which is a pretty large addition to the U-value. that assumes the metal extends all the way through the insulation, which it wouldn't. The SAP calculation looks great as it ignores this thermal bridging, but the reality is more complicated.

I wasn't suggesting you'd get better than 220mm of equivalent thickness of something of order 0.040. The 'overfill' was to make it stay put, but to be clear I'm not suggesting anyone actual does it.

Amazing to think of the weight supported by studs. If doubling up on something like SoundBloc, Each stud is supporting about 80kg of weight (1.3kN/m). Check you Structural Engineer's allowance for partition weight as sometimes it's only 1kN/m.

Loft roll isn't self supporting so would just collapse down over time whereas the more expensive ones do self support. That said I have often thought it would be easy to anchor Loft Roll in place and stop it sagging and so save a bunch. But as is often the case with such ideas, it's not going to be used as per the manufacturer's guidance and so BCO won't be happy nor the Warranty provider. If filling rafters (ie no air gap) another approach that might work and be much cheaper than the correct product would be to squeeze something like 2no. 150mm into the 220mm rafter. The compression might be enough to hold it in place. I spoke to a merchant years ago and he said some builders staple Loft Roll to rafters. They may have quoted competing against builders using the right stuff. I would be interested if anyone has done something like this.

@sean1933 It might be worth taking a look at OmniFit Slab 35 as it may be slightly cheaper than the FrameTherm 35.

I wanted to check the effect of varying Acoustic Roll thickness on sound and the headline is adding just 25mm is 5dB better than having none, but adding 50mm is a further 1.5dB better. It may be cheaper to upgrade the plasterboard than double the thickness of the Acoustic Roll (SoundBloc+25mm is better than WallBoard+50mm). The Gory details: Maddeningly, BG have changed their product selector website and it's near useless. Previously I remember you could select which studs and plasterboard you'd use but now its got all the detail codes instead of the stud type. It says "To see all Specifications that use a particular Product, please go to the Product page and look for the ‘Show me all specifications that use this product’ option." but if you select a specific stud type results include other types! Sadly the madness doesn't end when you download the CSV. Although the table includes stud type etc, the columns are messed up so the data can be in the wrong columns 😞 How hard can it be! I added a column that concats all the columns after the abutment one (as many use C studs for abutments but other studs mainly) checked if the concat contains the stud name I want and then filter. {EDIT: easier to use find on column B} Below is some extracts. The colours are Duraline orange, WallBoard white, Fireline pink, SoundBloc blue (red text if SoundBloc F), TileBacker grey, and Habito yellow. Multiple lines as different insulation options, the first of each group is no insulation. The first 5 are the 15mm Duraline with the following insulation (APR 1200 unless says): none (42dB), 25mm Isover Acoustic Partition Roll (APR 1200) (47dB), 50mm Isover Acoustic Partition Roll (APR 1200) (48dB), 80mm Isover Modular Roll (49dB), 75mm Isover Acoustic Slab (50dB) Other sheet types that have less options follow that order though (double check). 102mm Partitions with 70 S 50 C-studs: 97mm Partitions with 70 S 50 C-studs:

These are good prices for the current environment. What supplier(s) are they from?

Good advice, it's what we would have done months ago if it wasn't for Covid

If only 🙂 She'd be more interested in the bedroom than the kitchen though

Thank you for checking, very kind