Victorian renovation

[Brett_14]

Hi, 

I’ve purchased a detached Victorian property (c1900) and we’re about to embark on a renovation project. 
I’ll probably have a number of questions but thought I post the first one on here

 

To the rear of the property is a ground floor extension, c7 years old with wet underfloor heating. One of the rooms at the front of the house, adjoining this has old quarry tiles which look like they’re laid on a small layer of screed and just soil (maybe even just soil).
 

One of our aims is to make this room warmer and we’ve asked a builder to extend the underfloor heating system.

 

Plan is to dig up the floor, lay hardcore (100mm), a damp proof membrane, concrete (125mm), 100mm celotex, then the UFH pipes, then screed.

 

Does anyone see any problems with this method, especially with the potential to push damp into the walls? 
 

Ps we’re planning on re-laying the quarry tiles which I’m told are a good conductor for UFL, anyone have an opinion on this as well? 
 

many thanks

 

brett

Edited November 16, 2022 by Brett_14

[Dave Jones]

i have pretty much an identical project on the go, 1908 house. 9" solid wall etc

 

First on the list for us is internal wall insulation on 3 walls (4th is dropped for extension), 100mm celotex stuck and fixed including  cut 150mm ish all round the windows to ensure insulation is continuous to the reveals. 

 

Ground floor similar setup but im using 300mm of EPS as its cheaper than celotex and has a better U value. The 100mm wall insulation will be lapped right down onto it to make a fully insulated box.

 

We are also dropping all the internal walls at the same time so we can pozi joist the whole build including extension to make MVHR/plumbing/elec etc easier.

 

Obviously couldn't do this while living there so that is a limitation if you need to stay there during the refurb.

[jayc89]

40 minutes ago, Dave Jones said:

i have pretty much an identical project on the go, 1908 house. 9" solid wall etc

 

First on the list for us is internal wall insulation on 3 walls (4th is dropped for extension), 100mm celotex stuck and fixed including  cut 150mm ish all round the windows to ensure insulation is continuous to the reveals. 

 

Ground floor similar setup but im using 300mm of EPS as its cheaper than celotex and has a better U value. The 100mm wall insulation will be lapped right down onto it to make a fully insulated box.

 

We are also dropping all the internal walls at the same time so we can pozi joist the whole build including extension to make MVHR/plumbing/elec etc easier.

 

Obviously couldn't do this while living there so that is a limitation if you need to stay there during the refurb.

 

I'm doing very similar. 100mm PIR under the new floor slab, (likely) 50mm PIR on the internal walls. I'm purposefully going lower on the walls because I didn't drop the internal walls, so I'm worried about cold bridging/condensation at these points if I insulate too much.

 

In hindsight I should have dropped these walls and installed Pozi joists too as it's also making my MVHR planning much harder!

What method are you using to fit the PIR to the walls? Will your joists be refitted on the inside of the insulation? 

Edited November 17, 2022 by jayc89

[Dave Jones]

initially sticking the pir to the existing plastered walls with megastick and dropping in some thermally broken fixings where needed, then megastick plasterboard over and skim as normal.

 

https://www.phstore.co.uk/insulation-fixings/ejot-h1-eco

 

Joist hangers for the pozi is a compromise as there isnt a thermally broken hanger on the market, I've asked simpson! Did look at ledger board but not happy its strong enough so will use masonry hangers and wrap/foam them best I can to seal the ends.

 

The window reveals are hard work, grinding out a 150mm box all around them to make sure the insulation can be overlapped by the window frames.

 

Wonder if you could do similar on the internal walls where the join the external to get some insulation slid in without weakening them too much ?

[jayc89]

8 minutes ago, Dave Jones said:

initially sticking the pir to the existing plastered walls with megastick and dropping in some thermally broken fixings where needed, then megastick plasterboard over and skim as normal.

 

https://www.phstore.co.uk/insulation-fixings/ejot-h1-eco

 

Joist hangers for the pozi is a compromise as there isnt a thermally broken hanger on the market, I've asked simpson! Did look at ledger board but not happy its strong enough so will use masonry hangers and wrap/foam them best I can to seal the ends.

 

The window reveals are hard work, grinding out a 150mm box all around them to make sure the insulation can be overlapped by the window frames.

 

Wonder if you could do similar on the internal walls where the join the external to get some insulation slid in without weakening them too much ?

 

Interesting. If I was to do it again, I was thinking of doing something similar to this;

 

Sitting the ledger plate some blocks of EPS 300 or similar for it's compressive strength and sliding the PIR through the gaps. I just don't think I can justify ripping the entire first floor up now it's something like liveable. 

[Dave Jones]

i did look at that but unconfirmable hanging 80m2 of flooring, bathrooms etc on just a few screws through a ledgerboard.

 

My plan is to encase the end of the pozi as much as possible so  the wall insulation is as continues as possible.

 

It really does need an engineered solution as there are literally millions of solid wall homes unsuitable for EWI that at some point will have to be  modernised. Keeping an eye on simpson to come up with a thermally broken hanger.

[jayc89]

19 minutes ago, Dave Jones said:

i did look at that but unconfirmable hanging 80m2 of flooring, bathrooms etc on just a few screws through a ledgerboard.

 

My plan is to encase the end of the pozi as much as possible so  the wall insulation is as continues as possible.

 

It really does need an engineered solution as there are literally millions of solid wall homes unsuitable for EWI that at some point will have to be  modernised. Keeping an eye on simpson to come up with a thermally broken hanger.

 

Agreed.

 

Have you considered PUR spray foam instead of PIR boards? I've toyed with the idea purely because it should double up to also provide a more foolproof airtight barrier. I had a quote for someone to apply 75mm of foam and they charged, on average, £18.50/m2. 75mm PIR is approx £15/m2, unfitted, without tape etc, so the foam didn't seem crazy expensive. 

[Dave Jones]

not considered spray, im not a fan of it really. ill be taping all the joints prior to plasterboarding paying extra attention to the unboarded area between pozi's to get them tight.

 

I'll leak test before floors go down to track down any leaks.

[Brett_14]

Hi both, thanks for the replies. In my instance do you think it would be advisable also putting some internal insulation on the external facing walls (as well as insulating the floor and installing UFH)? Maybe 50mm as Jayc89 suggests? I’m concerned if I internally insulate I’d be trapping moisture and causing damp issues. I did first start thinking to do this but stopped after I read so many negative views about it possibly causing damp. 
 

Thanks 

[jayc89]

4 minutes ago, Brett_14 said:

Hi both, thanks for the replies. In my instance do you think it would be advisable also putting some internal insulation on the external facing walls (as well as insulating the floor and installing UFH)? Maybe 50mm as Jayc89 suggests? I’m concerned if I internally insulate I’d be trapping moisture and causing damp issues. I did first start thinking to do this but stopped after I read so many negative views about it possibly causing damp. 
 

Thanks 

 

I don't think there is a one size fits all answer to that question. There are so many variables; is your house pointed using lime? Has it been rendered? If so, with what? Are the ground levels suitably low? Are your drains and gutters functioning correctly? There are so many sources of damp that need to be controlled before it becomes a problem internally.

IMO, and I'm only a novice DIYer, moisture only gets "trapped" if it there's an excess of it (i.e. raised ground levels, broken drains/gutters) and/or it can't escape from either side (i.e. the external face is pointed and/or rendered using cement.