B&B+internal cellulose layer hybrid

[Olf]

Reading the forum it seems to me that the conclusion is that cellulose filled panels offer the best insulation, providing low U and long decrement delay, with thickness being the biggest drawback.

Well for my extension that is not an issue, but as it is going to be built along the boundary line on one side, and with restricted access to the back making lifting the panels a no-no, it fells like I'm stuck with brick and block.

I thought I could go wild with cavity width (say, 300mm), but now I got this crazy idea that the opposite could be done: to go with 100mm filled cavity (pretty much to satisfy minimum BR requirements) and add internal layer filled with cellulose.

Cost wise there is one more structure to erect, but being non-load bearing I should do with 600mm stud spacing, only 2 1/2 walls to add (2 sides + garden facing half being glass, 4th side existing house wall), boards go quicker than bricks and blocks and, all is diy-able. Insulation cost seems to be roughly comparable. But the gain would better temperature stability inside, so maybe luxury worth having at not a lot extra spending?

One thing that worries me in such hybrid is location of dew point: it would be brought towards the inside of the wall, meaning likely happening at the block layer. How bad is it?

Or maybe if the inner layer is thick enough, the whole brick&block structure would be 'outside'?

Anything else I'm missing? Has anybody tried something similar (eg renovation with internal insulation, being the same in principle)?

 

[Ferdinand]

It is easier to have a decent relationship with your neighbour such that you can work from that side for the short period you need.

 

With an appropriate benefit to them.

 

I hope you have this - better for all concerned.

Edited August 10, 2020 by Ferdinand

[joth]

On 11/06/2020 at 16:19, Olf said:

 

Well for my extension that is not an issue, but as it is going to be built along the boundary line on one side, and with restricted access to the back making lifting the panels a no-no, it fells like I'm stuck with brick and block

 

You can "stick build" (construct on site) the frame and then blow fill with cellulose, it's not a requirement to factory build panels for this method.

Indeed this is exactly what we're currently doing, our main contractor looked briefly into factory building them but even with our very basic square house it would have been a nightmare getting all the tolerances and angles exactly right to match existing so they're just doing it onsite. 

The old house is 60s cross wall construction and we've demolished and rebuilt both the curtain walls in timber, so it's only the supporting flank walls that remain as B&B. I really hope this won't make insurance a nightmare!!

Can share some example photos of the junction details if you're interested

[Olf]

1 hour ago, Ferdinand said:

It is easier to have a decent relationship with your neighbour such that you can work from that side for the short period you need

100% agree and I think we are lucky (the original post was made 2 days after we moved in, no relationship at that time except for annoying by keeping relocation Luton van on the street fighting for parking space).

But to some extent it was a 'thought experiment' as I'm sure there are some folks that for one reason or another would be limited.

 

1 hour ago, joth said:

Can share some example photos of the junction details if you're interested

Yes please!

Building an extension, not a hole house, my requests seem to be ignored by all the major solution providers - I'd be more than happy to have local chippy to erect the frame in situ

[Ferdinand]

1 minute ago, Olf said:

100% agree and I think we are lucky (the original post was made 2 days after we moved in, no relationship at that time except for annoying by keeping relocation Luton van on the street fighting for parking space).

But to some extent it was a 'thought experiment' as I'm sure there are some folks that for one reason or another would be limited.

 

 

Yep. It’s to do with giving appropriate compensation in cash or kind where they feel you have been sufficiently generous whilst you feel you have not been exploited. It might be a payment or eg providing a professionally designed and built shrub border over the bit of garden that your building project has trashed.

[joth]

3 hours ago, Olf said:

Yes please!

Building an extension, not a hole house, my requests seem to be ignored by all the major solution providers - I'd be more than happy to have local chippy to erect the frame in situ

 

Here's the extension frame going up, and now with windows installed and getting close to ready for warmcell, plus a close up of where the new extension frame meets existing cavity wall.

[joth]

Here's the front curtain wall mid-demolition, and post demolition with bottom half rebuilt

 

As you see, the main structural component front and rear is 300mm I joists