MortarThePoint

On the ground floor I have a gas membrane over the top of concrete and on the first floor I have hollowcore concrete planks as the floor. On both levels I'm going to have 40-50mm liquid screed with UFH in. I've started putting down 125um polythene* and it feels pretty pointless. Downstairs there is already an impermeable membrane. I'll discuss this with the screed guys and see what they think. Upstairs is different, but still feels like there could be something better. I don't have insulation on top of the concrete (GF it's below the 50mm concrete, FF don't want it as not worried about responsiveness). On the first floor, the hollowcore (HCF) is largely 'waterproof' with a few scattered holes. What have others done here. It's impossible to not have some voids under the membrane and it feels unnecessary. It occurs to me I could do some of the following as an alternative to membrane: Paint some form of sealant on the floor and add edge strip Apply a thin layer of self levelling compound (1-3mm) to form a seal and add edge strip Just fill any holes that would leak and add edge strip All would give a more intimate connection between the HCF and screed as well as being much faster than membrane. * https://www.toolstation.com/green-vapour-barrier-125mu/p86538

I did wonder about that, but when the roofers fitted a tile vent it took me a while to notice it

Bit of a tangent, but what do people think of roof mounted vs wall mounted bathroom extractors? I don't have MVHR.

I did ask before if I could jus have an AAV and he said at least one SVP needed although it's a single house and package sewage treatment plant situation

I'm sure a 15mm pipe would work by 75mm is the reg. (copied in my previous post).

For reference, I thought I'd add some extracts from Part H:

Which route would you take? OK not you yourself, but which route would you let the foul smells take. The Architects plan was to send the soil pipe down through the floor in the right hand corner of the bathroom (as viewed below) but we not have open space below now so don't want to put it there. As it's now going externally, we moved it close to the side of the chimney to reduce its visual impact, and that position is shown below. This is the furthest extent of the foul water system and so needs an SVP (not just AAV). We don't want to continue the stack outside and offset round the eave. We don't want the vent tile too close to the chimney so it likely needs to be towards the top right corner of the image below. I see two main options: Route the main stack to SVP tile vent connection as shown below. 75mm horizontal run at floor level junctioning to a 75mm vertical run up to the vent. Route a vertical run of pipe (e.g. 75mm) up the top left corner of the image below and the turn horizontally in the roof space track along and the back to vertical above the right hand corner and to the vent tile.

Interesting to see how these sorts of things are done in other countries. They made the hourdi blocks onsite. https://youtu.be/lF7aSes4gcU

An alternative shutter approach is to use some short lengths of narrow rebar, some wire and some OSB3 strip (about 150mm wider than gap. Pass a loop of wire through the gap and round the OSB. Secure the wire tight to the rebar on top of the planks. Do this at each end of the OSB. Then fill the created pocket with a cement ballast mix. Guess you could use timber rather than rebar if you the cut the wire later. Otherwise you can just leave the rebar in place

Yes, but was this because of using a concrete pour rather than a screed?

Cool shower waste. You did go for UFH under the shower. Was you floor concrete with rebar?

I don't know why but I had presumed the UFH would not extend under the shower. I'm not sure I'll do it. Other than your good point about the trap, I can't think of any pros or cons as the shower water will be hot.

Is it standard to have UFH under shower trays?

Looks the part. At £5/m2+VAT I'd rather DITRA though even if it's a little more expensive.

Is anyone else buying their screed at the moment? I'm typically being quoted about £350/m3+VAT installed based on 11m3 for Annydrite liquid screed, does that sound market rate? Not normally part of my daily shop, so less confident than some of the other commodity items.

Some options here: https://www.protilertools.co.uk/categories/materials/tile-matting Durabase is thicker (4mm) than DITRA (3mm) and about 10% cheaper. There are a couple of uncoupling mats that are less than 1mm thick and quite cheap (<£5/m2), but that's not much room to do a good job of uncoupling. If @nod used DITRA on his own house I think that says a lot.

Just reinforcement I think: https://products.kerakoll.com/en-GB/p/biotex

I don't know if the stuff below is any good, but I guess it doesn't decouple. Only £2.87/m2 though. "Kerakoll Biotex Anti Crack Matting is a reinforced anti-cracking sheet matting, for evening out tensile and sheer movements between the substrate and the surface finish. Also suitable for use as an anti-cracking product for tongue-and-groove hardwood floors on critical substrates. For internal floors. Previously known as Kerakoll Idrobuild Tex Matting" https://www.tilingsuppliesdirect.co.uk/product/kerakoll-biotex-anti-crack-matting#.YKO0bahKhaQ

I couldn't find it on the website either so called. DITRA 30m roll for £6.67+VAT / m2 as a starter. Thanks @nod.

This is one of those potentially overlooked costs. Can you get away without it, possibly. Would you kick yourself if you didn't use it and had an issue, definitely. As a self builder you have enough to worry about, so worth including. It does seem rather costly, but maybe I am looking in the wrong place. Looks to cost around £6/m2 or above. You have expensive tastes. Just joking, but it must be very good as I can't find it for less than £10/m2.

Your installers did better than mine then. Like I said, I chalked this up as a Covid consequence though as I'd have been all over it otherwise.

Yes that could work nicely. If I tucked the rebar into the core hole on the right hand side and onto the beam on the left hand side it would all hold well. Alternatively, I am thinking of leaving it to have OSB3 and SLC over the top and using the hole as a possible 'conduit' to route things along the landing as there is a smaller hole at the other end too. The SLC would be minimum 20mm thick which meets the requirements of most over timber (e.g. Weberfloor Flex or Weber 4310). Covered in carpet any small cracks at the SLC/screed interface wouldn't matter. Not so sure what I'd send along there though.

You also end up with some unintended openings. I have to work out how to close this one (200mm wide) within the 40mm of screed depth that is going over the top.

Interesting reading. My experience has taught me two things: 1. At spans under 5m you can have big holes knocking out two steels with no issue. 2. When they install them it is easy for the planks to drift out 50mm or so in the direction perpendicular to span, putting your opening in slightly the wrong place. OK for services a pain for something like a chimney (I had a 700mm chimney passing through the join in two planks and had to shrink the chimney to 650mm). Make a checklist of dimensions to be checked as they install. I'd have been all over them if it hadn't been for Covid. 3. You'll forget some holes. Haven't tried drilling anything larger than 25mm, but that was very easy.

Not ideal, but I would have to have a box channel to pass the pipe along the wall that would need to be internally 40mm above finished floor and externally around 50mm above finished floor depending on the finish on the box channel.