low_and_there

@JohnMo under the floor isn't the only way, no - I had at some point got to that conclusion but now you ask I am actually not 100% sure that I recall why that was. It could just as well go through the external wall and in. Given what @IanR has pointed out about needing a very deep trench in order to come up vertically, perhaps that is altogether better...? To your questions JohnMo, the outside unit is going to be placed 3m from the external wall but in total about 9m (as the crow flies) to the hot water cylinder. If it comes in through the external wall it would probably need 5m outside and then about 3m along the wall inside.

Looking for a bit of help: We're about to install an insulated raft foundation (300mm of EPS with a 100mm concrete slab on top) and have planned for all the pipework under the insulation excepting the future route for the ASHP pipes and electricity supply to it... I was planning on putting in a route for pipes to be inserted through later on when the ASHP gets installed but have failed to get very far with an installer - is there a reasonably safe size of ducting I could use to enable future insulated pipes from the outside ASHP to be routed through under the slab and into the thermal envelope of the house? For the electrics I am just going to put in a big pipe with rodding access for cabling to be pulled through in the future. Am self-managing our renovation and like most renos it's not gone to plan or budget and all my planned dependencies have been turned upside down. thanks in advance

thanks very much @Mike and @ETC - "Architectural Masonry" is a keyword I was lacking in my searches. Much appreciated

Hello all. I am looking for a conc block that we can leave unfinished as it's for a wall that we can't get to the outside of to render. BC have said such 'fair faced' external-grade blocks exist but i can't find any from searches online - I have called a couple of manufacturers who have confirmed they don't make them but also believe such products do exist. Anyone familiar with particular conc blocks that meet this criteria? Thanks

Where do you think the right place is in the sandwich? Or are you proposing simply trusting that the overhand pointing will be decent enough? Appreciate other suggestions if you have any. Not keen on the tanking idea myself but seems better than not having a weatherproof outer skin

Good point about the blocks not being cracked. Will inspect! Yes forgot to call out that there will be a VCL on the inside of the PIR. Fire-rated pb is stipulated by BC. Yes the gap is tiny, hence the proposal to use a tanking solution to reflect that it is going to be impossible to guarantee it won't get stuff in it. It's not perfect. I don't think anything in this situation is perfect. It's not been suggested by the Builder but rather building control have indicated they've seen this used in similar situations successfully. Other suggestions welcome but anything involving leaving a bigger gap is not an option.

This sounds interesting - is this a 'method'? The bricklayer has said he'll do his best and also try to keep the gap clear of mortar but he was keen to flag that it won't be perfect - if there's a method he's perhaps not heard of for making the joints better then that would be interesting! Thanks @Redbeard

Hi folks, looking for help on a couple of questions re a new external wall we're building in the extension. For context, the wall is being built within cms of another wall so we can't render externally. Have been advised to apply a tanking slurry to the inside (a bit like you would in a basement) to acheive weatherproofing. Two questions: 1) In this context, is it worth using thermally broken wall ties or is the fact that the tie will be on a Timber stud effectively act as a thermal break? Looking to achieve a high thermal performance. 2) Is it safe to put the PIR straight onto the coated blockwork or should we leave a void? If so, how many mm for that void? Thanks! --- Proposed fabric build up from outside to in: External air (50mm max) Dense fairfaced conc block (100mm) Coated with a tanking slurry PIR - 125mm Timber studs 47mm filled with 25mm PIR lined with fireproof board plaster finish

No, you don’t need vents for a ground bearing slab. Unless it’s adjacent to a floor void that does need ventilating. And therefore you need to have a route for ventilation to get through.

Given the rest of the ground floor has a ventilated void I guess I thought may be good to keep consistent airflow instead of just telescopic vents under a slab

Hi folks, looking for thoughts on which approach makes more sense for our relatively small extension: it’s about 26sqm total - a mid terrace kitchen and side infill. SE had specified a slab on the basis that he thought it was a slab there when he jumped up and down on the floor. But actually on lifting up the floor it turned out to be half slab and half suspended timber. The ground conditions underneath are basically soil (elsewhere on the ground floor it’s more clay). And it’s not clear how much would need to be dug to remove the soil layer… possibly a lot. We need to put vents and quite a few pipes underneath the new floor and given the soil situation we’re wondering if block and beam would actually be more appropriate. Thoughts appreciated.

Following some of the reading on this site, we're interested in using the insulated raft foundation approach for our extension. Our SE denies all knowledge of insulation and wants nothing to do with it so I am looking at getting one of the providers to do the design work. Trouble is this is for an extension and in order to knock out the wall in question, to then do the dig and lay the raft, we first need to support the floor above, which means we first need to put one steel post in the ground - this will have to therefore be done using a trench foundation rather than sitting on the raft itself. To do this then, how do we best insulate that steel post so it doesn't create a big thermal bridge? Is it simply a case of lining it with EPS from the base? Or using something like an Armatherm thermal break at the base... Any suggestions? thanks

what kind of sealant are you thinking @Tetrarch? Thanks

Yes this is a good point! Thanks

The neighbour's house is about 50cm lower than ours (the road is on a hill). Looking at the SE's drawings for the Party Wall build (our neighbour shared them with us when we were on good terms) the strip foundation they have put in does not extend at all on our side (excepting that it is obviously underneath the party wall itself. If the houses were level with one another then your point would be valid and present a problem, but it seems that the foundations don't project... That is actually a bit weird isn't it! Instead of strip foundations we're going for 'raft' foundations (as mentioned in OP), so no need to project 150mm.