lizzieuk1

Thanks Iceverge, food for thought then.

Would it be an option to use rockwool slabs between the I joists if we couldn't do the blown cellulose. Looking at thermal values they look very similar. No idea on cost comparison though so, any info on that would be helpful.

Yes we could, and will, work in the drier weather (so long as the uk summer plays ball!) but with a 1.7+m trench in clay I'm not convinced it is any cheaper than the raft. Did a quick high level costing and there was very little difference. Will do a more detailed cost once I hear back from the raft suppliers to see how things compare. It's a nightmare trying to decide as everyone has different preferences and all perfectly viable reasons for those preferences! Will have to make a decision at some point or we'll never get our regs drawings submitted!

Yes, but the upper 400mm is topsoil so easier as less clay to excavate - after digging a large 'pond' out in the field we've experienced the grimness of excavating the clay too 😆

It's a fair point JohnMo but, we feel, as we will likely do much of the works ourselves that, the detail may be simpler to achieve. Also, SE has said on the hedge side we will need 1.7m deep foundation (if medium vcp), with all the usual hassle of clay boards etc, not to mention the sticky mess of excavating all the clay! I think a raft may be a better solution.

Yes, I think you're right, the greenraft looks similar to isoquick- hadn't noticed that last week when I looked at it. Will make contact with AFT and have a chat, need to make sure we start things in the right way, literally the foundations of the project! Thanks Ian!

Is that because Isoquick use a level, constant 200-300mm concrete slab rather than an integrated ring beam Ian? Have had a high level cost from Greenraft for material supply, worth asking them for design?? My worry is the SE doesn't have enough experience and will just design the easiest option, which, inturn will mean its sub-optimal. Don't want to upset the SE but need a diplomatic way to tell him we're going elsewhere for the raft 😬

OK, so the SE has come back to say happy to detail a raft for us. I asked for an example he has done before but, his reply was: "I have done insulation below ground bearing slab for the industrial building working in the previous company and I do not have such a detail. I have been running my company for 6 years and no one from my 1200 projects has done XPS below the slab. It's a shame because this is a correct way to insulate the building. You should assume 200mm XPS if you wish to have a well insulated building." Then he's put a link to Isoquick as an example of a foundation he feels is ideal. Now, we're not suggested he can't design one but, a bit concerned whether it will be the best option. Help! Should we go to one of the raft suppliers or elsewhere to get it designed?

Many thanks Iceverge, that's a great post.

Found these and I think the may do 3g so will enquire.

Thanks Nick, its not easy, I've been trawling for hours hence the post, thought there may be someone on here who's done similar.

Yes, that's what I was meaning when I mentioned mock sash, there's some much nicer ones too that actually look like sash windows but are on standard casements. But, I can only find 2g ones, hence the question of is 2g(lower u value) with good AT preferable. Just wondering how a 2g compared to 3g will affect our efficiency.

That was my thought too but, are there any good options for the Georgian proportion windows?

I had a feeling that would be the response 😆

On a slightly different note, any opinions on which is more impactful, u-value or air tightness?? Looking at windows, likely options are upvc 2g mock sash or (possibly) 3g or traditional sliding sash - though struggling to find any with 3g as an option! Thinking mock will have far better AT than trad sliding.

Hi all, So currently scaring ourselves with the new build budget and trying to find a good solution for windows. We have a georgian type build design, so sash windows looking to feature. However, aware of the poor air tightness and, it seems, lack of 3g availability for a sash. Wondering if anyone has any good solutions, not averse to a good mock sash in wood effect upvc, but are there any 3g versions? Ideally not timber as, going forward and getting older, maintenance has to be a consideration.

Ah that's good, we're in Lincs

Crikey that sounds pretty good Nick, so we could build to 1st fix and then get them in without needing to do any parge coating at all?

Think the blown cellulose is our preference, we don't have shallow pitch and will have blue slates & solar but still like the cellulose option. Only issue may be if we can find a supplier so we can diy it, though not sure how much cost saving to be had compared to supply & install option.

Amazing, thankyou 😊

It is used quite widely in other countries though so, there must be positives that drive the usage.

In preference to posi joists? Then underlined with insulation for cold bridging?

😊 thanks

Wowser, thanks Nick for such a thorough run through of all that! As you say it is worth asking the question re cost and a conversation around woodcrete to see if that approach is a cost effective/practical option or if parging first would be better. (Obv they will want to sell as much product as they can so I guess critically appraising their answer is in order) The one issue I could see for us, is that we have been looking at a posi joist roof structure & blown cellulose which, sounds like it may not be suitable for that system. The cutting & fitting of pir between rafters (and now a need to tape all sides) is so painful, not to mention the cost, so we're looking for a better way!

It sure is! Thankyou buildhubbers, you are all a vast knowledge base and I really appreciate your time with my questions!