bissoejosh

I've seen the MBC system and would be very tempted if our build were simpler. My understanding is they only do full builds and we have a lower GF built separately for a variety of reasons. Certainly looks a great product in the right situation however. I was hoping i-stud might prove a decent compromise between a standard frame and something like the MBC. We've got a mixture of render and cladding, both on vented cavity but no outer block / brickwork much like yourself. I've seen the frametherm, infact I think I priced either this or dritherm so good to hear it's nice to use. I suppose using an engineer and sourcing direct could work for the frame, although I'd still prefer to outsource as a whole if possible. Did you specify 100mm externally for a specific reason or was that set by the overall wall thickness? Just wondering if we went for a conventional frame what would be the minimum external insulation needed to avoid issues with condensation/cold bridging.

Having gone off SIPS for a variety of reasons I had hoped to use an i-stud system for the timber frame element of our build. One attraction is the lack (or reduction) of thermal bridging which hopefully eliminates the need for an external layer of insulation - keen to avoid celotex or similar if possible and keep things breathable. This simplifies the build and gets it weather tight that bit quicker - important for our DIY fit out. I also have a preference for flexible insulation as it will also be a DIY job - a 220mm istud full filled with 0.032 glass batts looks to give 0.12/0.13 U value which is better than my target at an acceptable wall thickness. Unfortunately none of our local timber frame firms seem to do i-stud frames which surprised me. Other than Touchwood (quoted - v.expensive) does anyone have a recommendation for an istud supplier? We're in Cornwall. Alternatively how badly would a 190 or 215 solid timber frame suffer from cold bridging and if the answer is badly what level of external insulation would be need to avoid the problem? As always, opinions / alternatives welcome!

thanks, that matches my thinking. I'm sure with a bit of care I can get a decent junction....

Sadly ICF is looking like a no go for us. Mortgageability is really important and our choice of a timber frame first floor is already throwing up barriers compared to a 'traditional' build. To then add in ICF seems to be asking for trouble - rather depressing but life goes on. This brings us back to my original question about the the best way to seal a timber deck with frame above onto a masonry cavity wall. As mentioned the masonry element will be 400mm thick with 200mm full fill batts so still a handy amount of insulation. Joists onto a wall plate seem straightforward enough but to then span the cavity makes the air tightness detail difficult. Would an adaptation of the 'tony tray' still work if it lapped the end of the joists and ran back in, under the sole plate to meet the vapourblock providing air tightness on the frame above? Rim board + protecting the joist ends seems doable with the correct amount of external insulation + full fill between. I can offset the frame above to make it all line up externally. As always advice very much appreciated! BlockFrameJoin2.pdf

All really useful, many thanks. A long conversation with Alan at Polarwall today has moved things forward. I've one question-mark over mortgages which I've posted in the ICF forum but hopefully it won't be an issue.

Hi, we're seriously considering using Polarwall for the ground floor level in our new build with timber frame or SIPs on top. Has anyone who used Polarwall or ICF in general had any issues obtaining mortgages? Research suggests that some lenders consider ICF standard construction, others non standard. As a country we seem so far behind in accepting new methods of construction... Given our upper level is timber framed we're keen to keep at least part of the building favorable with lenders if at all possible. If ICF is going to cause headaches it'll be back to block cavity again for the ground floor. thanks

Purely based on a floor with free flowing air under it being less efficient than a ground bearing slab etc. Every build is a compromise and ours is that we need to have a suspended floor for a large part of the house - more than made up for by the plot itself. The tetris system does look v.good, waiting to hear more from the supplier having sent drawings etc. I have to say that the more I read about ICF it seems to fit nicely, & from what I can gather it's OK with lenders generally. Also, just found your blog - cracking project! Looks like you found Polarwall a good experience - what levels of insulation and core thickness did you opt for?

I actually spoke to Alan at Polarwall last week as they are fairly local to us. I need to follow up today. Not sure how ICF could support the beam and block running away from walls at the upper level - can some sort of shelf be formed outside the external skin of insulation? All the details I've seen show something similar but on the warm side of the wall. Agree about its DIY potential plus it's inherently more airtight which I like.

Firstly hello from Cornwall, Having browsed for the last year or so both here, GBF and on the old ebuild site I have to say what a fantastic source of info such places offer. Myself and partner are about to begin our self build I'm hoping someone can help with a particular question. Our plot is unusual in that the majority of the house is at 1st floor level (onto garden) and extends outwards from the lower level spanning an access alley between the house and a retaining wall. Because of the site elevations the upper level (where external to the lower level) will be on a B&B floor (tetris most likely) which needs to meet the lower level and sit on the outer skin of blockwork. Therefore we need to build the lower GF level in block - proposal is full fill 100mm block - 200mm glass batts - 100mm block (7n) all parge coated with a foundation detail matching Denby Dale / Golcar. Whilst I don't like block it works at supporting the upper level, is DIY able and I can focus on the detailing - sites like tonyshouse etc help greatly with this. At first floor level we want to use either timber frame or SIPS and whilst we aren't looking for passive standards (the B&B effectively kills this), efficiency is high on our list. Quite simply does any one have a detail showing a well thought out join between a cavity block lower level and timber / sips upper that focuses on air tightness and continuity of insulation? In particular I'd like to build to the outer leaf line of the lower level to maximize internal space and avoid an odd external detail at the join. External finishes are render lower GF & horizontal cedar / larch cladding 1st floor. My line of thinking was to build straight off the outer leaf but 100mm blocks won't work with 172mm SIPS which makes me think a platform construction is the way forward... Whether we opt for SIPS / timber frame (quotations are currently out and the same question is being asked to suppliers) I intend to mitigate the sole plate bridging issue with a course of thermal block under the plate plus 40mm of XPS sheathing extending 250mm above and below. Hopefully this will suffice. Please excuse the very DIY attached detail, still learning sketchup! Any help much appreciated! Josh BuildHub1.pdf