G and J

Whoo hoo!

My close knit family of 18v Makita batteries means that I’d never think about anything else. The instant start stop, the lack of fumes, lack of noise do make it so much easier. We won’t need a brushcutter at the new pad (we declared war on ongoing maintenance requirements) otherwise I’d have already gone twin 18v. As for using non Makita batteries…. :-0

Crumbs, funny how different things can seem when a more interesting and illuminating viewpoint is highlighted. You should consider doing this for a living @Gus Potter 🙂 I think of concrete as totally inflexible and solid, but nothing really is. If I think about two people standing on a thin sheet of ply on a lawn, no one would be surprised at it bending if they stood right on the edge. But if they moved in a bit it would bend less. Shock! The more I think about this the more I like strip foundations.

Husky chainsaws and Stihl kombi brush/hedge cutter for years. In my garage I had lots of 18v makita drills/routers/saws/etc. Decided to try battery based hedge trimmer. So impressed. All electric now, apart from the Stihl stuff I’ve not yet got round to selling. Will never go back to petrol. If you’re going to be using the brushcutter for a few years I’d strongly advocate making your life easy and going electric (and I’m with onoff, makita stuff is fab).

Re: Cladding - dunno, might be, certainly the concern about cladding in general won’t help. Might be more about the British obsession with masonry, which I have been guilty of in previous years. Re: Mortgages - dunno that either. Underwriters aren’t ones to share their thinking, and they focus generally on volume and risk. So if their criteria accidentally disqualifies the most fabulous builds which only constitute 0.17% of the market why would they worry. I was recently surprised to hear of a Hanley self build mortgage which gives slightly better terms but is only applicable if you are at wall plate. My guess is that that is because most self builds that fail do so before wall plate.

We’ve been looking at mortgages, including self build, standard and lifetime. First thing we noticed is that some self build mortgage lenders aren’t so keen on lending if you already own the site. Second thing we noticed was that some mortgage companies inc. self build mortgages are particular about the type of build. Hence we are now looking at reducing the amount of wood cladding to less than 50% and we are putting in a blockwork outer skin for just over 50% of the external walls. We’ve had useful guidance from a specialist broker, so don’t be afraid to talk to one of those.

OK, J just found out what perpends are and now I understand your point @ADLIan . So maybe the TF200 Thermo will help a bit. I’m minded to derate the insulative contribution by a third….

PS. Julia is wondering it’s taking you longer answer all my stupid questions @JohnMo than it would to build our blooming house! (I do appreciate the help though guys).

This is (an attempt at depicting) the issue that’s on my mind. The expansion and contraction of the frame due to varying temperature and moisture level won’t be matched by the thermal expansion and contraction of the PIR. So the frame shrinks, the PIR pushes on the plasterboard and the screw digs in a bit. Then in winter the frame expands and the PIR doesn’t and the plasterboard suddenly has a small gap behind it and pop!

Noted, ta.

Understood re nails. Re the air gap question, I’ll draw it out.

So with screws need I worry about maintaining an air gap behind the plasterboard?

From the LABC manual…. of course it might help if I knew what a ‘perpend’ was. 😕

I’m busy contrasting lots of different wall build ups, some of which worry me from a danger of plasterboard fixing popping point of view. We have history. 20 years ago we had builders put a room above our garage, they used battens with PIR in between, and they nailed the plasterboard on, and we got a good few pops, which still occasionally happen even now. I have wondered whether it’s caused by the combination of batten shrinking/expanding with moisture content making the PIR push the plasterboard - to start with they appeared the same thickness. It is possible I might replicate that scenario in some places - 140mm PIR in a 140mm frame then VCL then plasterboard. In many areas we are likely to put another layer of PIR on the frame, and/or a service void. But is 140mm PIR in a 140mm frame asking for trouble? Do I need to put a slightly smaller thickness of PIR in there?

And I’m guessing that a stiff and chilly breeze blowing over the shiny breather membrane nicely cools it and therefore almost completely negates the insulative effect. Reading the LABC manual re ventilation required I understand it to require ventilation openings in the plinth equivalent to the size of a whole brick every six bricks. Assuming corresponding openings at the top that’s got to make the cavity a mini wind tunnel.

Ta. But I was totally correct of course. I really did show my ignorance as that is b obvious lol

I’m thinking back to school physics - yep, literally half a century ago. I remember that dark materials both radiate and absorb heat radiation more than light ones, so could it be bidirectional? I get the need for an air gap as otherwise conduction would occur, and ventilation would mean convection would occur, either undermining the insulative effect.

Ok I’m really going to show my ignorance now…. What are MIs?

[Sound of penny dropping] So the VC foil works when inside a service void at reflecting heat back into the house if the reflective side faces in. It had never occurred to me that a substance of composite could have different u values for different directions. More study required.

Ubakus DIY? Is that the paid version?

Now why couldn’t I find that - I thought that was the case but I couldn’t find it definitively. The LABC manual says in one place that 50mm empty cavity is needed but elsewhere it talks about insulation in the cavity - of course they may mean partly filling a bigger cavity. Where did you manage to find that about not fully filling a timber frame/masonry cavity?

I suspect the difference lies in the ‘rot’ of the inner skin. A block inner skin won’t rot but a wood one might.

Is that block -cavity -block? I know that one can fully fill the cavity in a block built house. Trying to find guidance re timber frame/block skin is boiling my head!

I’ve been trying to research this, and the LABC manual does refer to cavity insulation but it’s not clear whether the clear 50mm void needs to be maintained. So if it does I might as well have the extra layer inside the frame and leave the frame to breath as much as possible.

We’ve decided to try and change our design to make our house more easily mortgageable and insurable. We are hoping to obtain permission to reduce the percentage of the house covered in timber cladding, increasing the amount of render to just over 50%. The other change we won’t need the planners to agree, we are going to have a block skin for the outer leaf wherever we have render, which is most of the ground floor. Ours is a narrow site so the wall thickness has always been limited, which is why we are looking at these two products. The build up we are thinking of from inside to outside is: 1. Skim (3mm) 2. Plasterboard (12.5mm) 3. PIR (25mm - this will be channeled where needed for cables) 4. VC Foil Ultra 5. 140mm frame filled with 140mm PIR 6. 9mm OSB 7. TF200 Thermo 8. 50mm cavity 9. 75mm block skin 10. Cement render (15mm?) If I’ve understood correctly the VC Foil Ultra has an R value of 0.78, which helps. But the TF200 Thermo I’m not so sure about, it might be 0.77. I believe we have to have a 50mm void between frame/breather membrane and the block skin. What I’m unsure about is what level of ventilation the cavity needs, and whether that will be enough to undermine the thermal characteristics of the TF200 Thermo. I also don’t know how the cavity drains, in case of condensation on the inside of the blocks or rain ingress. Here’s the data sheet for the foil: https://glidevaleprotect.com/app/uploads/2021/09/VC-Foil-Ultra_FINALAPPROVED_0624_Screen.pdf and here’s the data sheet for the breather: https://static.prod.cmostores.com/uploads/attachments/4/protect-tf200-thermo-data-sheet.pdf In theory if the cavity isn’t really ventilated then the above wall build up gets me to a U value of circa 0.13, which we can live with. Am I wasting money? Are there better products? I’d appreciate any comments/corrections/better ideas/etc.