Insulating an eaves space

[Geoff Flegg]

Yet another insulation question........

My house is a Victorian three-storey affair, with attic rooms with sloping ceilings - so we have no loft as such. We re-roofed the house recently, and took the opportunity to fit insulation - although it is a pig of house to insulate!

The floor area of the attic rooms is less than the floor below, as you have the area around the edge of the building where the headroom tapers to nothing - the eaves space - which has lightweight lath & plaster walls blocking it off from the attic rooms.

The insulation is generally in between the attic ceilings and the rafters, but we have eaves space which is accessible and is used for storage. Despite using breathable roofing membrane, the Building Inspector insisted on vent tiles being fitted for all the enclosed spaces in our roof - of which there are plenty. This means we have a minor gale blowing into the eaves space, and cannot insulate these spaces at rafter level.

The eaves space being uninsulated is not a problem as such, as it's only for storage, much as a loft. The question is though is that we are losing heat from the bedrooms underneath. I can solve this in one of two ways:-

1 - Take up the floorboards in the eaves space and stuff ordinary loft insulation / thermafleece in between the joists. Will help, but given the depth and the cold bridge effect of the joists it could be better. Floorboards will also be a pain to lift.

2 - fix Kingspan / Celotex slabs over the floorboards, and put some cheap chipboard flooring over that to spread the load for me crawling about and for all the junk I keep in there. Will insulate extremely well, better than option 1, but am I asking for problems with condensation forming on the underside, affecting the floorboards / joists ?

Anyone got any better ideas?

Geoff

 

[Geoff Flegg]

Have I actually managed to stump the collective brains of PPUK ???

Or is everyone just sooooo bored of insulation questions that they're losing the will to live?????

Geoff

 

[Moo]

As far as insulation is concerned, my brains are permanently stumped.

I just thought I'd respond to your message as a way of getting it back up to the top of the list, where Those Who Know about such things will be more likely to notice it.

 

[Lime]

My opinion for what it's worth.
I would choose the take-up-the-boards option so that the insulation can be in direct contact with the ceiling.
If you cover the boards with kingspan AS WELL the insulation will be even better.
However if you only cover the boards then there will be an air space under the insulation (between boards and ceiling) that is just as likely to be part of the gale as anywhere else.

You could choose to only take up only a few boards and install a granulated insulation which can be pushed into areas not opened up.

 

[middi]

If you use, as you suggested, celotex or similar on the existing floorboards ( say 50mm or thicker) plus cheap chipboard above this to walk on, you should achieve an exellent insulation factor.

Use aluminium tape to seal the edges of the insulation and complement any oakward-to- access corners with rockwool.

There is no chance of any condensation forming in the lower part of the insulation or the upper ( colder part) as this is ventilated.

 

[Lime]

you should achieve an exellent insulation factor

Yes, between the attic space and the floorboards.
What insulation factor that exists between the floorboards and the upper ceiling surface is a different matter.
As the void under the boards is ventilated the insulation will not be very much good at all for the bedrooms below.

 

[DaveBrigg]

Lime, do you have any more details about the granular insulation referred to in your first post? I've got a similar problem to Geoff, with sloping ceilings (lath and plaster) beneath a slate roof. The roof has a breathable membrane, so I assume that ventilation will not be a problem. I can access the space between ceiling and slate, but don't want to try pushing kingspan or similar down in case it dislodges the plaster.
Thanks

 

[Lime]

DaveBrigg, Vermiculite or similar is what I would use for between the flooring of the loft and ceiling if I wished to use a granular insulation.
However I would NOT use it next to the breathable membrane under the slates as it is quite heavy and will compact itself under gravity pressing on the membrane.
It can also get wet and cause problems with moisture retention.
Any granular insulation when inserted in a sloping or vertical space is likely to compact downwards and be difficult to keep in place.

I think kingspan is unsuitable for the situation you have as well.
It is much too stiff.

Rockwool or similar would be better but should have been put in when the tiles were off!
Whatever you use I would avoid contact between the membrane and insulation.
The membrane should be able to breath and have a circulation of air behind it.

 

[DaveBrigg]

Many thanks for that Lime. I had arranged with the builder for insulation to be put in when the tiles were off, but then suddenly in one day it had been stripped and the membrane fitted - hence the problem. (I think they were trying to do it between rain showers).
I may try one of those very thin foil laminates, and see how easy it is to slide down.
Dave

 

[Nemesis]

Foils:

http://www.periodproperty.co.uk/discussion_forum.htm

 

[Geoff Flegg]

However if you only cover the boards then there will be an air space under the insulation (between boards and ceiling) that is just as likely to be part of the gale as anywhere else.

Good point. I remember being quite shocked at the draught that was blowing about underneath the first-floor boards when I took some of those up recently, so chances are the next floor up will be as bad if not worse.

Thanks everyone for the tips.