Victorian flat insulation - again

[trancera]

Hi all,

Sorry if this is a bit of a repetitive subject, I have read dozens of threads related...

I have a flat, and for the purpose of this thread in particular a large chest freezer for a bedroom!

The ceiling is quite high 8ft+, it has original cornice and has a bay to the front, with slopes either side.

The best I can think to do is line the vertical walls with 12mm (I know yuck) Celotex and 12.5mm plasterboard where that will meet the cornice in an ok fashion.

The slopes and bay window area would take 25mm celotex+ PB.

Other than taking off ALL of the plaster work is that the best I can achieve with what I have?

Currently the slopes+bay are slate+felt+boards+about 8 inch of air plus lats/plaster, and thats it. I have tried to work out what the U value is and what I could get it to try and get a % reduction in loss. struggling a bit though. advice on understanding this please.

I added 200mm insulation ready for this year cross ways over the original insulated in between beams (so now like lattice over beams so no air flow down beam sides) ... i don't think there's any benefit in anything up there now? Hence doing the slopes to bounce heat towards the flat well insulated above part...

Any help really really appreciated, i'm already burning gas all night and hot water bottle,duvet and cover over top

Thanks.

 

[freddiemercurystwin]

Adding 12mm Celotex is almost not worth bothering. Better than nothing I guess but you'll still need a wooly hat. If you want to retain period features you sometimes have to live with period heating.

 

[alittlerespect]

Hi

To sort your bay out you should consider removing the wall plaster and lathes, then install 100 to 150mm thickness of PIR insulation between the studs (finished flush with the inside face [room side] of the studs) and then use a sandwich board similar to Kingspan K17 around 50mm overall thickness directly fixed to the face of the studs. This last bit will stop any staining of the wall at a later date due to temperature differences between the timber and the insulation. If cost is an issue you could reduce the thickness of the insulation between the studs to 50mm but this should be the minimal thickness used between the studs.

You will likely need to form a trim detail where the insulation meets the windows, possibly a 25mm quandrant of timber will do, or if you have a frienly timber merchants or joinery shop in the vicinity they will be able to cut down a piece of timber to suit your requirements! You can sort this out once you have installed the insulation materials.

If you use PIR insulation you will not have any problems with condensation as PIR is very vapour resistant. However, as a precaution you may wish to install a vapour barrier across the face of the studs prior to installing the K17 to this end you could use a 'foil' material which will provide some additional thermal benefit as well as being vapour resistant.

Then you are left with the external facing walls of the room. As you have described 12.5mm is a bit drastic, but it will still provide around a 50% reduction in heat loss!

As a general rule, I reckon that every 25mm thickness of PIR insulation reduces the heat loss by around a half. For example a basic solid 9" wall will have a U value of around 2.1W/m2C adding say 25mm of insulation would reduce the heat loss to 1.05W/m2C adding a further 25mm (50mm total) of insulation would then reduce the heat loss to around 0.5W/m2C giving around a 75% reduction in heat loss through the wall.

Regards

 

[trancera]

Thanks for the replies, and I totally understand that 12mm isn't great at all, but must be what 10x better than no resistance to heat loss at all?

I would get rid of the 'features' if i could, but I cannot.

As for the bay, that's a bigger and more expensive job than I hoped for which I guess financially it'll never pay back, though i am sure will pay big in comfort!

I will have to consider it carefully as It'll be messy and I'll be sleeping on the floor elsewhere while its being done

As the bay side walls are only a small % of the walls though is it really worth it if the slopes lose much more (at least twice the area here)

Spot on with the wood trim, thanks.

 

[trancera]

Looking at it, insulating the flat roof area of the bay (dormer) would be easier to do heavily, which is about 1/2 the total bay area (the sides lopped off at 45 degrees).

I might compromise on 50mm top 25mm sides as most bang for buck and least mess. According to what you say that ought to reduce the bay loss by over 1/2 (excluding window - sash/case dont get me started)

Thoughts please?

 

[alittlerespect]

Hi

Other people have used an insulation thickness of 25mm and have noticed significant reductions in heat loss, and if you go with what you are proposing to do you will get more than a 50% reduction in your heat loss.

As you have commented insulation between the studs would cause some drastic disturbance to your day to day living and to be honest such activity would only normally be carried out where a building is unoccupied and is being rebuilt to meet the stringent requirements of Part L of the Building Regulations.

You mention sash windows, and I would just like to say that in my opinion sash windows are the best designed windows ever invented, their only downfall is that the older single glazed versions can become a bit draughty, and the combination of heat loss and draughts can dramatically reduce their thermal performance. The way to overcome the draughts would be to use a draught sealer fixed to the closing edges of the staff bead. B&Q do such an item, check out 'www.diy.com' and search for 'sash window draught proofer' - simply nail in place on staff bead.
This should reduce draughts significantly.

For the thermal aspect either go for some heavy quality curtains, or consider some secondary glazing. Theres a good article on sash windows at the following web site: www.buildingconservation.com/articles/sashwindows/sashwindows.htm

Regards

 

[trancera]

Thanks respect,

Your help is much appreciated. The windows are modern DG sash actually, but some work on draughts would be good - curtains can move. I hope to make some 'thermal' blinds to effectively seal off the window area at night.

I understand why people report such a benefit from a small amount of insulation - the walls have large drafts in them. Plaster is useless in terms of insulation and behind it is cold air (5c?) lapping any heat away.

I do wish i could do the whole room in 25mm. I can't. But I can do 10% in 50mm, 30% in 25mm and the remaining in 12mm (including the internal walls, little cost and they are cold internally). All of course sealed and covered by a layer of plasterboard. I can easily see how it will half the heat loss, in combination with some decent carpet underlay - the floor is so cold!

At that point I feel an area heater would maintain a reasonable overnight temperature - rather than abusing the full central heating. Payback, who knows 5+ years but in terms of the rooms feel, well a much better place to be.

Thanks.

ps for anyone searching / reading re loft insulation, its really cheap at b&q at the moment. Paid for by energy companies, i.e. your bills, so get ur loft topped up for £15!

 

[alittlerespect]

Hi

On a personal note I would not bother insulating the internal walls at least not between adjoining rooms as there should be minimal temperature differential between the rooms and as such there is no direct heat loss.

When it comes to the floor there are various insulating products available (Knauf and Jablite come to mind) only problem, the minimum thickness of insulation is 25mm plus you would have to allow for a flooring grade chipboard on top of the insulation which would add 18mm, plus add for underlay and carpet, say 15mm giving a total thickness of 58mm. The issue becomes one of whether or not you could live with losing 58mm off the door height, or whether or not you could raise the door height to accommodate!

The flooring grade insulation has similar properties to wall insulation, wall insulation being slightly better, however, adding 25mm of insulation to the floor would reduce your heat losses.

As you have mentioned with the additional insulation you should find that the property becomes more affordable to heat.

Regards