Full fill in very severe area of driven rain

[Iceverge]

27 minutes ago, Lewis88 said:

Unfortunately I warranty is a must for me, my partner is adamant. I’m not opposed to making the cavity larger with more insulation but the NHBC strictly rules out full fill with fair face masonry.

 

Ah, if there's no other reason for the warranty I think you're probably just buying yourself a placebo. 

 

I just did a Google of "nhbc forum payout". 

 

It doesn't make very reassuring reading. 

 

31 minutes ago, Lewis88 said:

Iceverge are you saying that I should do the stone and glass gable as the following internal block, full fill insulation, external block (with render applied) then a cavity and stonework? If so that could work. I suppose that the render would mean that it is no longer considered ‘fair faced’ and just had a stone skin?? 

 

Yup that would work practically. 

 

33 minutes ago, Lewis88 said:

I’m really not au fait with any other form of building than brick and block, but that all any of the trades do around here. Could it be easier to do this part in timber frame? My architect tells me that build systems can be joined/interchanged.

 

There's certainly advantages with sticking to locally used building methods but surely timber frame isn't considered unusual anywhere now? Good systems like MBC are excellent but some cheap ones are poor.

 

Personally I would ditch NHBC and just ensure its build properly by a competent and conscientious builder. You'll have far more comeback in reality. 

 

[joe90]

1 hour ago, Iceverge said:

Personally I would ditch NHBC

They have a reputation of not paying out, despite that mortgage companies still recognise them but there are many others, as I said I got a retro one when I had to sell.

[Lewis88]

@Iceverge and @joe90 you both make a really good point, about the warranty being not worth the paper it’s written on. I think my wife sees it as a comfort blanket. I believe I read that you could buy an indemnity should I ever want to sell (if before ten years).

 

timber framed has been discussed but I’m not too keen on the idea if I’m honest. I have this preconceived idea that it could rot even though I know that this isn’t the case. This house will be passed to my children so I want to make sure that they never have to put their hands in their pockets. 
 

I don’t think there is really any valid options for me to have an NHBC warranty with what I want so I think that’s probably the best idea, I have enquired about other warranty providers. 
 

is there a sweet spot in cavity sizes for things like lintels etc? Thinking that a larger cavity is probably wise. My only concern with going larger than 150mm is the cost and availability of thermally broken lintels.
 

I had seen the Denby Dale passive house and I think that’s what sold me on the idea of having full fill mineral wool. It’s not a million miles from what is considered the norm and it looks easy to do. 

[joe90]

57 minutes ago, Lewis88 said:

is there a sweet spot in cavity sizes for things like lintels etc? Thinking that a larger cavity is probably wise. My only concern with going larger than 150mm is the cost and availability of thermally broken lintels.

I plumbed for 200mm cavity as middle ground from building regs to full passive , regarding lintels I used concrete internal lintels and brick arches in the outer skin. No real reason to have a lintel crossing the cavity and mine was dead cheap, if you don’t want arches then use single skin lintels in the outer skin. Just make sure a DPC crosses the cavity with weeps over doors and windows.

[Lewis88]

@joe90 that sounds like the way to go. as I’ve only been reading about all of this for half a tomatoe season, I didn’t even know you could have lintels that only span one skin. I’m presuming they rely on the wall ties to make sure that the walls stay plumb? Out of curiosity what did you put in the top of the window reveals to stop the insulation falling through?

[Iceverge]

Separate concrete lintels on bother skins here. Very cheap. About €40/window in 2020. 

 

We used OSB window boxes but installed the windows beforehand to the outer skin only. 

 

Regarding width we did a 250mm cavity with stainless steel ties from Vartry in Wicklow Ireland. 300mm would only have cost about €1200 more. Money that would have been well spent in hindsight. What ever you do, go for a multiple that allows you to install 2x layers of insulation. IE. 75mm X 2 or 150mm X 2 to ensure the joints are all staggered. 

 

Am easier method of closing cavities might be to use a wide airtight tape returned to the inner leaf and then a J bead screwed into the window to slot in some plasterboard. 

 

 

 

 

[joe90]

Yes the wall ties do their job and cavity closures all round.

[Lewis88]

Thanks everyone, I’ve decided to up the insulation to 200mm, we don’t have our current house too warm (usually about 19-20c) and will have a small room sealed log burner for the coldest of days. 
 

so the OSB holds the first layer of MWB and then it’s back to business as usual for the wall ties? Did you choose to use the basalt rods or just stainless ones? 

[joe90]

Good on you for bigger cavity and insulation. I did rough calks on the use of stainless ties over basalt and the benefit was very small for much bigger cost so used stainless. Frankly using metal lintels spanning both walls was a far bigger heat sink than stainless ties.

Edited October 8, 2023 by joe90