LiamJones

Hi, thanks for the replies. I initially posted this with the idea of using roof trusses to span the width, supported only by external walls. I was then curious if I could make do without any internal solid walls, but not sure about the lateral support requirement. I’ve since instructed a structural engineer who’s drawing up some plans for a couple of load bearing internal walls (to provide lateral restraint too) and steel ridge beam. I’ll likely go with this approach.

I’m not sure? In theory, the bottom of the cavity is way below damp, so it doesn’t really matter which way it goes?

I've done a bit more reading, and a thread on green building forum seems to suggest it'll be fine regarding interstitial condensation.

FWIW, i'm also installing a whole house MVHR.

Thanks for your comments @Russell griffiths @Conor @MikeGrahamT21 I want to use the same build up for the whole building, putting ICF on the end of a block cavity bungalow complicates things. It's only a small extension and i;ve got brick layers lined up to start in a week. I originally posted this more to check block choices and the dpc/weep vent requirements. To me, it just seems simpler to keep it all the same. Especially given i need to solve this problem on the existing bungalow. Regarding interstatial condensation, i modelled it using 0c/20c with no condensation. -5c/20c does have some condensation, but appears to be significantly less than the existing and within acceptable ranges, fully evaparorating in the drying season. If i swap the aerated blocks on the inner leaf to solid blocks, i can further reduce the condensate, and move the condesation point to outside the cavity. This reduces the uvalue by 0.02, but within regs (0.18 for new elements on exisitng dwellings) I'm no expert on interstatial condesation, but it all looks okay and within range. what am i missing? Thanks, Liam.

The logic behind some choices; - the 70mm cavity, this is to allow the extension to match the existing cavity and avoid a tricky detail/thermal bridge between new and existing. - the external wall insulation, this will be being added to the existing walls, so it makes sense to run it through flush on the extension. N.b, plasterboard to be dot and dabbed to aerated concrete block, struggled to model it. I've also not included weep vents, i don't think i need them?

I’d get rid of the suspended floor and start again. With 200mm below the joists I’d assume you’d have atleast 300mm with the timbers out the way. You’d have to inspect what the sub base is like and work out how much, if any, hardcore you need to put in before building up with insulation and concrete/screed. You can put a dpm down too and cover up the air bricks.

Can a bungalow with external walls of 17m x 7m, with no load bearing internal walls, provide adequate lateral support to the 17m walls by posi-trusses spanning the 7m? Or are butress walls required along the 17m walls? Thanks, Liam

thanks, how are you doing/have you done your internal walls?

What did you use?

My concern now with just the concrete is how easy it’ll be to get level enough. Screed obviously solves that problem.

Interesting, have you got a link to the product/company you used?

hi @HughF, I’m getting closer to this and learning more. I’m now trying to work out the spec for the concrete that UFH is laid in. Some do 100mm, some more. Some use rebar, some use fibre, some use none. Can you shed any light on your choice to use 125mm concrete with no reinforcement?

Great post, thanks. Where did you put your DPM?

You can offset lower performing glazing with higher performing glazing. E.g a 5m2 door 0.2 under notional with 10m2 of windows 0.1 above notional.

25mm pug mix on top of DPM?

Plans have just been approved, the delegated report contains the following text; In my circumstances, I didn't need to submit any CIL forms, so all is good here.

Hey planners have said should be issuing my approved planning notice Monday which is great news. it’s a householder planning application for the demolition of the garage, an extension and a loft conversion. All in its under 100m2 additional space so is not liable for CIL. If the planners haven’t asked for any CIL forms, E.g Form 1, do I need to do anything else?

The jsp fp3 ones are decent https://www.amazon.co.uk/ForceTM8-Respirator-Complete-PressToCheckTM-Filters/dp/B00ZCOFHM0

so if you go 100mm slab on top of insulation you don’t need screed? Is it decent enough to tile on (if done well)?

Im a bit confused by this, is a concrete slab not required? I’ve always though it’s was 100mm min concrete slab (either over or under insulation) plus 70mm ish of screed on top?

For £177k I think you could get a pretty sweet off-grid setup

Ah sorry, I’ve got my wires crossed. I was talking about planning permission as a householder app rather than full planning. Building Control id go full plans regardless, it’s actually cheaper in my area than notice.

Ah okay, I was reading about some ecology survey only being possible in May (I think), to do with when certain animals are ‘active’. Didn’t want to have to wait until next May!

Do I definitely need full plans? I recently saw a a demo and rebuild as a householder app that got approved in my district!