Insulation: Converting 2 flats to original Edwardian house

[Triggaaar]

Ok, here goes. After living in our Edwardian flat for 6 years, we are at last going to knock the dividing wall down and open up the original house. Not a big job on it's own, but with the top two floors being empty, now seems like the right time to do all other jobs that are worth doing.

Here are the plans (internal width = approx 7.6m):

Ground floor (Day room is part of a future extension, and the courtyard will probably become part of that extension too. Bath will become WC. 2 Halls will become 1):

First Floor (Kitchen will become en-suite)

Second Floor (Dresser will become en-suite)

There are so many things for me to consider, and experience has taught me that I'd be better to ask for advice here before I start

The main thing I'm unsure about is how to improve the insulation (cavity walls have been filled, flat part of roof and stud walls in eves have been insulated):

Possibly put celotex between the ground floor joists (already done in the living room)
Do something with the sash windows? There are 23 that would need work, so it could be too expensive to be worthwhile. The options would be replace them with double glazed wooden sashes, or add some brush draft excluders, or paint some shut, or add some glazing to the existing windows (and now open them) :?
Add external secondary glazing to stain glass windows (the windows on 1st & 2nd floor landings) - no one would see it, is it possible to add glazing to reduce heat loss?
Insulate the sloping ceilings - perhaps remove the lath and plaster and use celotex.
If doing the above effectively seals the house, add some mechanical ventilation (I know nothing about this)?

I'd really appreciate any advice on the points above, or anything else you think might be a good idea.

Many thanks
T

 

[Froggie]

I have a big old 1830's built house without cavity walls so have been through some of this already.

You're on the right lines with the floor and ceiling insulation but be careful if removing lath and plaster ceilings as the laths do provide more structural rigidity than plasterboard does since it spreads the load better across the trusses so you may find that the roof sags a little after doing this. You can fix wooden braces across prior to boarding in order to mitigate it.

The best quote I had for reinstating 6ft x 3ft sash windows in hardwood was £1,450 each so this is going to be an expensive option for you. I did buy one uPVC sash unit (£400) for a room that I had to renovate quickly but it offended me so I ended up replacing it with hardwood. As you suggested, you can run brush strip along the areas where the gaps occur (new wood sash units seem to have this as standard) but you can still lose quite a bit of heat through the old glass. A number of companies produce a 7mm thick double glazed unit which should be a direct replacement for the glass already in the casements and gives better thermal performance. Secondary glazing would also help but I would still seal the existing windows as well as possible before doing this.

You will also lose quite a bit of heat through chimneys but sealing them up usually creates damp problems. If you're not using chimneys then point the roof stack, cap the pots with rain hats and seal the internal openings with a board that has a trickle vent in.

Hope this helps

 

[Triggaaar]

be careful if removing lath and plaster ceilings as the laths do provide more structural rigidity than plasterboard does since it spreads the load better across the trusses so you may find that the roof sags a little after doing this. You can fix wooden braces across prior to boarding in order to mitigate it.

I had no idea about that. Is it possible to just put celotext and new plasterboard straight under the existing lath & plaster (obviously fixing to the rafters)?

The best quote I had for reinstating 6ft x 3ft sash windows in hardwood was £1,450 each so this is going to be an expensive option for you.

Yep, over £30k is a bit expensive - it wouldn't be saving that much on heating bills.

I did buy one uPVC sash unit (£400) for a room that I had to renovate quickly but it offended me so I ended up replacing it with hardwood.

:lol:

As you suggested, you can run brush strip along the areas where the gaps occur (new wood sash units seem to have this as standard) but you can still lose quite a bit of heat through the old glass. A number of companies produce a 7mm thick double glazed unit which should be a direct replacement for the glass already in the casements and gives better thermal performance.

We have those 7mm ish units in the lower half of two sashes at the moment. Ironically, they'd be the only sash windows that don't need improvement, as they'd become internal windows. I think the previous owners did it more for security than insulation, and they didn't do the tops of the windows because it they'd fall down when unlocked. Still, I might be being stupid, but I think that's an option. If the reduction in heat loss was significant, I wouldn't mind permanently closing a lot of the sashes (do you really need 5 opening windows in a room?).

You will also lose quite a bit of heat through chimneys but sealing them up usually creates damp problems. If you're not using chimneys then point the roof stack, cap the pots with rain hats and seal the internal openings with a board that has a trickle vent in.

I forgot about the chimneys

Hope this helps

Yes, thanks, appreciate it.

 

[Froggie]

You can get thermal plasterboard which is basically foam insulation bonded onto plasterboard. It's around 40mm deep and is easier to work with on ceilings than separate insulation and plasterboard. It's probably a better option since it doesn't disturb the existing structure but be sure and find your screwing points before trying to put it up unless you like the swiss cheese look

The slim double glazed units are quite a bit more thermally efficient than standard single glazing as they reflect some of the heat back into the room but you would have to replace the sash weights as they are also quite a bit heavier.

Your priority should be to minimise draughts in the first instance, insulate next then look to the window glass.

 

[Triggaaar]

You can get thermal plasterboard which is basically foam insulation bonded onto plasterboard. It's around 40mm deep and is easier to work with on ceilings than separate insulation and plasterboard. It's probably a better option since it doesn't disturb the existing structure

Are there no condensation issues to worry about if putting the insulation straight on the lath and plaster?

Your priority should be to minimise draughts in the first instance

Where should I look for drafts, and what should I do to prevent them?

Thanks

 

[AndyT]

Just picking up on one of your questions, I had some good advice on secondary glazing over stained glass in this thread

https://www.ukworkshop.co.uk/forums/secondary-glazing-pondering-t76212.html

 

[Triggaaar]

Just picking up on one of your questions, I had some good advice on secondary glazing over stained glass in this thread

https://www.ukworkshop.co.uk/forums/secondary-glazing-pondering-t76212.html

Brilliant stuff, cheers! I'd be happy to go for the same solution.

Have you had any condensation in there yet?
And have you any idea if it's made any difference?

 

[AndyT]

Just picking up on one of your questions, I had some good advice on secondary glazing over stained glass in this thread

https://www.ukworkshop.co.uk/forums/secondary-glazing-pondering-t76212.html

Brilliant stuff, cheers! I'd be happy to go for the same solution.

Have you had any condensation in there yet?
And have you any idea if it's made any difference?

No and no! But we don't seem to have had any properly cold weather since I did the job.

For what it's worth, I live in a similar aged property and a couple of years ago decided to overhaul the original single glazed sash windows by fitting draught strips from Reddiseals. I found that I could just about deal with a single pair of sashes in a day, removing them, stripping off the old paint, ploughing grooves, applying quick drying primer and re-fitting with new cord and beads. I only had six pairs to do, which was quite enough. Was it worth it? Again, it's hard to tell, and the old glass is very thin, but I think it has made some improvement.

 

[Froggie]

You shouldn't have any problems with condensation or moisture when putting the thermal board over lath and plaster as long as the lath and plaster isn't get wet from a leaky roof above.
For anyone using this on external double brick walls you do need to have an air gap behind by using some sort of frame or rail system.

To look for drafts I used a smoking match around window frames, external doors etc... when the weather was windy.

If you find gaps in opening windows this can be caused by something as simple as runs/lumps in the paint forcing the surfaces apart. Once you sand these back flat check again and if there's still a gap you can use self adhesive brush strip if the gap's wide enough or, for narrow gaps, a fresh coat of paint to build up the surface. Just remember that the wood will contract in the cold weather when selecting the thickness of the brush strip. The key to using the self adhesive brush strip is to ensure that the surface that you stick it to is flat and clean or it will come off.
If you sand back to bare wood anywhere then you will need to seal the area with paint.

If you find any rotten wood anywhere then remove anything which crumbles away easily and treat the remaining wood with a wet rot wood hardener. Once this has dried, fill the area with an epoxy filler, sand back to a flat, level surface then prime and paint.

Draughts coming from the edges of window frames where the frames meet the wall will need sealing round internally with a suitable silicone but you will also need to check the pointing around the exterior of the window frame and either re-point with mortar or run a thin bead of exterior frame sealant round if there are hairline gaps caused by the contraction of the wood. It's best to check for hairline gaps during the cold weather.

I would still sort out the existing windows even if applying secondary glazing as the air gap between the existing window and the secondary glazing provides some of the thermal benefit.

Draughts around external doors are similar to fix, make sure everything is flat and closes tightly. Check the that the lock mechanism holds the door tightly against the frame and adjust if necessary. Brush strip can be also be used here. If the door doesn't close into a frame at the bottom then a Sammy the Snake draft excluder will add a bit off class to any interior :wink:

 

[Triggaaar]

Excellent, thanks for all those tips.

You shouldn't have any problems with condensation or moisture when putting the thermal board over lath and plaster as long as the lath and plaster isn't get wet from a leaky roof above.
For anyone using this on external double brick walls you do need to have an air gap behind by using some sort of frame or rail system.

I don't understand the difference - why do you need a gap if doing it against brick walls, but not for a sloping ceiling?

Thanks

 

[Froggie]

Excellent, thanks for all those tips.

You shouldn't have any problems with condensation or moisture when putting the thermal board over lath and plaster as long as the lath and plaster isn't get wet from a leaky roof above.
For anyone using this on external double brick walls you do need to have an air gap behind by using some sort of frame or rail system.

I don't understand the difference - why do you need a gap if doing it against brick walls, but not for a sloping ceiling?

The gap for the wall installation on cavityless external walls is to avoid direct transfer from moisture in the wall. The lath and plaster ceiling already has a void behind it and shouldn't be getting wet unless the roof is leaking.

 

[Triggaaar]

When sealing an old house, is there ever any need to add mechanical ventilation, as they do on eco builds?

 

[Froggie]

When sealing an old house, is there ever any need to add mechanical ventilation, as they do on eco builds?

I'd only add mechanical ventilation through ceilings in bathrooms and would add an inline heat exchanger through which the input and output stages pass.

You shouldn't need any other mechanical ventilation if you have trickle vents in the chimneys.

 

[owenmcc]

Have you considered using wood wool board, or wood fibre board as opposed to celotex? Has the benefit of insulation, breathability and offering a surface upon which to plaster.

Owen

 

[Triggaaar]

Have you considered using wood wool board, or wood fibre board as opposed to celotex?

No, I know nothing about either. I'm after advice. Maybe I should be looking elsewhere?

 

[owenmcc]

This is a link to a company my old firm used as a supplier, they also have good documentation on the application and benefits of 'wood wool board' and 'wood fibre board'.

http://www.lime.org.uk/products/boa...dingwood-wool-board/buildingwood-wool-boards/

There's also some great information from Historic Scotland, who tried a variety of insulation upgrades to old properties and then monitored the outcomes.

http://www.historic-scotland.gov.uk/technicalpapers

Technical paper 19, page 49, provides the summary of u-value change based on the interventions made for ceilings.

This has more pictures:
http://conservation.historic-scotland.gov.uk/summer-school-energy.pdf

I've worked with a bunch of people who deal with older properties and a good rule of thumb seems to be: If it was designed to breathe, let it breathe.

 

[Triggaaar]

Thank you all for the advice. Looks like work could start in a week, so I best order some materials

I think I will go for an insulation and bonded plasterboard solution, straight on to the existing lathe & plaster - except where the existing lathe & plaster is in poor condition, in which case, I'll take it out.

You can get thermal plasterboard which is basically foam insulation bonded onto plasterboard. It's around 40mm deep and is easier to work with on ceilings than separate insulation and plasterboard.

When you say 'foam insulation', do you mean like Celotex and Kingspan?

I'd only add mechanical ventilation through ceilings in bathrooms and would add an inline heat exchanger through which the input and output stages pass.

Do you mean adding an inline heat exchanger for every bathroom? I've never done anything like this, could you post a link to the products you mean?

This is a link to a company my old firm used as a supplier, they also have good documentation on the application and benefits of 'wood wool board' and 'wood fibre board'.

....

Thanks for all that - I had a quick look and I'd be quite out of my comfort zone, and think I should stick to plasterboard type stuff for now.

 

[Triggaaar]

I need to order some insulation bonded to plasterboard - if anyone recommend a product and supplier, it will be much appreciated. Most of my search results are for large pallets, when I only need a few boards.

Thanks