Converting a single skin to double skin

[Ben Weston]

Hi all,

 

We've just bought an 1870s cottage (with a horrible 60s extension but that's not relevant here as it's being removed) which we are almost completely gutting and renovating.

 

It was originally built out of Norfolk Reds and has since been pebbledash cementitious rendered. This will be taken off and we plan to render it in lime render, repairing the brickwork where necessary. The cottage doesn't have any particular damp issues but I'm keen to 'double skin' it as part of our renovation. I realise I will lose ~150mm on the external walls but it'll make it more saleable (mortgages, etc) and warmer.

 

In terms of achieving this in the most space efficient way, am I right in thinking we can add a stud wall internally with a 100mm cavity + insulation? Does it need to 'tie in' to the external wall as in modern builds? My other consideration was that the cavity will not be ventilated – is this OK or do we need to provision for this? All the floors are being dug up and re-laid in case there's anything that can be done while doing this?

 

Any and all advice welcome!

Edited August 6, 2021 by Ben Weston

[ProDave]

This is a serious reply.  Consider it as a knock down and rebuild plot.  It could well be cheaper and quicker with a better end result.

[tonyshouse]

I like that too, if you go for internal I would go 140mm sheet insulation plasterboard or equivalent lining mechanically fixed to masonry, insulate ceiling min 400mm quilt and floor insulation 

[Ben Weston]

2 hours ago, ProDave said:

This is a serious reply.  Consider it as a knock down and rebuild plot.  It could well be cheaper and quicker with a better end result.

 

Yes, that is being seriously considered. I can't get the sums to come out cheaper but it's still a serious consideration at this stage, if only for the VAT saving.

[Ben Weston]

2 hours ago, tonyshouse said:

I like that too, if you go for internal I would go 140mm sheet insulation plasterboard or equivalent lining mechanically fixed to masonry, insulate ceiling min 400mm quilt and floor insulation 

 

Thanks. As a follow on to the reply above, it's a complete re-roof and new floors job too. All said and done, it's really only the external four walls that will remain and, as above, they're not great.

 

My main concern is budget. If we decide to knock down and rebuild (which I accept is the better route in terms of end result), that's a VAT saving but also brand new foundations, demolition costs of the house, full rather than householder planning, etc. The VAT saving is swallowed by those additional costs and I can't see how it's quicker?

 

I could be completely wrong so very open to opinions. I certainly accept that many/most would opt to just knock it down and build anew. Unfortunately, we're up against both budgetary AND time constraints. Time moreso.

Edited August 6, 2021 by Ben Weston