Adam2

Am I correct in thinking that this perimeter insulation strip used on the exterior of a floor screed is there for insulative benefits and not to do with expansion? If so, with all my external walls being EPS I can avoid having to install this? The floor build up if it matters: concrete slab, dpm layer, PIR, slip membrane, UFH pipes, 55mm screed

Thanks @Mr Punter looks very nice. From the pics it looks like the posi-joists stop at the wall and the extended beam is what continues meaning you had both a nice detail and one which was easier to block in. I guess I could install exterior ply to the sides of the posi-joists then in-fill - bit of work there mind with I think 17 joists at 1.2m projection.

The joists are not yet strapped onto the wall plate so could be lifted (not easily mind) to allow this but I'm not sure how that would help in this scenario. On the outside face would the membrane do out under the joists and be then secured onto the ply deck? If so the membrane could also be secured onto the outside of the steel beam and achieve the same, though I wanted to avoid wrapping the joists like this due to possibility of any condensation (or other moisture even if from an installation defect) within this space then being trapped rather than dropping into the soffit/soffit vents. But maybe I misunderstood the Tony Tray application here - I did look it up and see how it applies in "regular" scenarios

Thanks @Iceverge we're sticking with warm roof I think as bit late to change that now. The joists are all a precise width and the space between top/bottom timbers is of course the same so I was thinking we could make a production line - getting there cut on a jig could be relatively quick and accurate to make them precisely to size. In our warm roof the issue of course with the ply being the VCL is that it is above the joists so we would have this issue (the waterproofing/insulation co) will be installing a vcl over the timbers in their own scope (price agreed so can't really remove and may be needed for warranty anyway) Maybe I could install a long roll of earthwool running through the joists across the width of the building maybe in 3 layers and thick enough so it is pushing into all the open space with PIR fixed inbetween the joists as per oriignal plan - may be a big quicker that fitting teh smaller pieces

Hurray - building the roof! It's a warm roof construction plasterboard posi-joists (225 deep) 18mm ply vapour control layer 150mm PIR (avg) single ply membrane edge detail will be aluminium (Tag Fascia and ali soffit with vents for any moisture to drain out) The roof - see pic, projects over the steel beam and I'm trying to work out the best way to stop this being a route for cold air beneath the insulation. Am thinking I could cut blocks of PIR inside the clear between the top and bottom timbers of each joist directly above the wall EPS + a thicker block of PIR or EPS in the gap between the joists. Is there a better way? Under the joists I was thinking to use an airtight VCL stapled to underside of joists with tape over the staples and with double sided tape to adhere to the steel and the EPS interior walls. To help with accommodating light fittings I plan to secure the VCL up the inside of specific joists to provide extra fitting space. I guess it is either this kind of approach or we deal with air tightness by really carefully detailing around the joists and taping this to the underside of the ply and down on the back of the steel beam (or insulation we'll install on the back face of this. Maybe this is a lot more economical than this additional airtight VCL running under the whole of the ceiling on this floor - about 80m2 Would be great to see pics of any similar installations.

Yes - to have some interesting impact I think he needs it to actually flood under the building!

Ahh great, looked to me like the lower semicircle was plaster not the fitting. Cheers

Nice but how do you get a nice plaster finish on the reveal/edge of plasterboard? Looks like could be a pain and slow to get a nice finish

Yes, different programme to usual. Not a house to my taste and a lot of money and pain for the outcome. But as long as he's happy...

Ahh I knew I was missing something. This (sushi school)will bring our budget back on track. Or maybe Aliexpress instead seeing as I'm short on time. Came across as a great couple and expect they'll have an amazing time living there

Any of you seen the Chichester episode of last week? All looks pretty amazing but no matter how much work he did himself and how smart they were about using their money £658K...really? 70K on windows alone??? Is this 658 budget possible

Thanks - maybe will wait until joists in and take a look at routing

A rough image that may help explain. Ducts come up through a services opening in a dressing room

I've an abundance of 150mm PVC duct - bonus from an auction so this is essentially free as I'll never use it all. Considering my ample supplies I was thinking that for the top floor of my house I could use this instead of a manifold + multiple semi-rigid ducts. There's 2 bedrooms and 2 bathrooms so figured a "Y" connector on the supply/extract then run the 150mm duct to the required locations. One concern I've seen mentioned is potential for noise transmission - the ends of the ducts will be about 10m each from the "Y" so about 20m apart. Not sure if anyone has anything at all similar but would be good to hear if the noise transfer is likely to be a real issue with this setup. If I do go this route it'll save 2 x manifolds and about 80m of semi-rigid duct so seems worth looking into (though accept a bit more work on joints and maybe some faff with routing)

Have a look at the air supply/extract positions to ensure you're getting air to move across the rooms - eg bedroom put it towards a corner opposite the door to avoid areas which will have limited air movement - that's at least what I was advised, am sure there is always some movement so no need to go to extremes.

Ahh I understand - no this is about placing the MVHR in the garage nit using it to provide fresh air to the garage - that should make more sense now. TBH - MVHR in this thread is really a red-herring as only mentioned in passing as the only thing in there that may generate any heat which will probably be lost through unwanted ventilation anyway

The ducting isn't a cost issue I have more than I will ever need thanks to a recent auction ? If the box is well insulated why is it a waste of time as you still get the air filtration though accept heat recovery may be less efficient?

Many thanks @Iceverge v helpful will be following that path then. I had planed a VCL beneath the insulation - think you may have possibly missed that on the message above The joists are all posis with metal webs so that will help I think with allowing flow across the width of the garage. I can put a full length soffit vent along both the front (above the main door and the top edge of the flay roof) and the rear or separate vent grills but the full length may look a bit better.

Just meaning no other planned appliances etc in there like a fridge that may generate heat. Figured the MVHR may, through the fans, create some small amount of heat that would be constant so may influence the environment a little - not thinking it will "heat" the garage so to speak

Appreciate comments on the above to make sure I'm not overlooking anything

Thanks really interesting - waiting for the first Grand Designs to feature one ?

Looks really interesting for a single floor structure - though not sure I'd be 100% happy in a 80mph wind though. Interested to understand why you think it is safer than ICF. Had a v quick look at one of the videos and it said it was an EPS house. An ICF house with the EPS lined with plasterboard I imagine (& hope !) is a fairly safe structure in that the concrete is robust to fire and the plasterboard will provide reasonable protection before heat builds up to allow occupants to evacuate. Why is an EPS house (not sure what is used for structural integrity to connect house to foundation etc) any safer than an EPS concrete house? 20K to build a house though is a bargain ?

Thanks, will look at the cost difference and take a punt. 2 of the floors are 300mm thick concrete slab so can't believe they'll move anywhere, maybe the upper floors on the precast (which are also a fair bit smaller) could be more of a case for the extra security in the matting

We're about to build the garage - hard to believe I actually typed that!!! Originally I wasn't going to insulate it as it will never be used for much that needs keeping warm - it's attached to the side of the house with an access door in between. But, I figured maybe look at the cost options anyway. The roof is 225mm deep joists, dimensions about 6m x 6m. Final layer is waterproof single ply membrane. Walls are mainly cavity which will have 70mm full fill glass fibre insulation. For the roof I figure I can go with: Cheap glassfibre stuff maybe 100mm between the joists with a gap above and form some ventilation holes to exterior - not sure how many I'd need? Beneath this - would this be suitable for the VCL? Do I just staple this into the joists which will then support the insulation (well maybe they will friction fit) until I install plasterboard ceiling? Then above the joists just some ply and the single ply (installed by more competent others) Knauf Earthwool 100mm (R=2.25) £1.57/m * 36 = £56 (or I could go crazy and have 150mm) Alternative of a warm roof - install my ply deck, install maybe 50mm PIR which needs to be tissue backed so not sure on cost (or could lay ply over foil backed PIR if cheaper) then single-ply membrane Recticel PIR (foil) (R=2.25) £7.20/m *36 = £403 I know a warm roof is generally preferred but unless I messed up with the numbers it will save me a hell of a lot having a cold roof construction in the garage The main garage door will be insulated but fully appreciate the temp will not be amazing just trying to stop it getting mega cold. The heat source in there will be an MVHR - I was planning to make an insulated box for it but if the garage is insulated maybe will be beneficial to let the small amount of heat it generates go into the garage? Or maybe it's best being kept close to the MVHR to aid heat recovery efficiency? Also wondering now what to do with finishing the walls - S&C plaster or line with plasterboard with a VCL behind it.... too many things to think about and it's only the garage ? Outside walls will be rendered if that matters.

How do you determine if matting or priming required? based on the product specs or the room size/shape? Am interested as cost is pretty high for adding matting if not needed. I'm thinking 50mm Cemfloor on 150 PIR on a concrete raft and upper floors 50-70mm on 25mm PIR on precast planks (bit uneven so may need some levelling first). If I can avoid mapping and not have a big worry over tile cracking that would be great!