Room in Roof Insulation

[Eddman]

Hi,

I have decided that my turn of the century mid terrace house will be cold in the winter! We have ground floor, first floor and then rooms in the roof with flat ceiling (loft space above) made of lathe and plaster ceiling, then part of the ceiling is sloping - again lathe and plaster with roughly 100mm deep rafters, then the timber stud walls with a void behind them to the external masonry wall.

My idea for the loft space is to leave whatever thin insulation is there and roll out 150mm loft insulation with another 100mm layer at right angles. I do not want to board it out or anything (don't want to add more weight to what i'm sure is over spanned joists!) so will just literally lay the insulation and leave it.

On the sloping ceilings, i don't really want to disturb the exisitng lathe and plaster as it will be a lot of work and very VERY dirty. What is the best way to get up to or close to building regs? The roof is just rafters with ba\ttens and then slates - no felt or membrane or boarding.

On the walls i have the same dilemma - either take off the lathe & plaster, then insulate and then board and skim - but the dirty job of removing the lathe & plaster worries me!!! hahaha.

Thanks for any help any of you mightbe able to provide me....

Eddy

 

[chirpychippy]

Your best bet is to put 100mm between the floor joists "if they are 100mm deep then 150mm over at 90 degrees.

As far as your rafters and the lathe and plaster walls/ ceilings are concerned, if you want to insulate to current BRegs then you have to remove lathes and plaster.

Sloping ceilings is:-

100mm celotex between rafters and 50mm over with a 50mm air gap.

You would have to baton rafter with 2"x2" timber, fit 100mm celotex leaving 50mm air flow gap to the back then counter baton with 2"x2" at right angles and fit 50mm celotex, your supposed to use Alluminium tape to cover all joints as well, then board and skim.
The walls are 100mm celotex between and 20-30mm over.

That's the building regs down south, they may differ elsewhere.

 

[Eddman]

i suppose the quilting material is not high performance and therefore will not be able to get sufficient thickness between sloping rafters?

I am looking at saving money you see, on initial costing (for materials) i have come up with;

Loft insulation roll - 200mm thick = £120 + 100mm thick = £90 TOTAL = £210
Celotex - 100mm thick = £468
Knauf insulated plasterboard - 27mm + 12.5mm = £320

This does not include for the stud walls - it is getting expensive.......


OH - and will i need a vapour barrier in the sloping ceiling part - where will this go - between celotex and knauf?

thanks again
Eddy

 

[chirpychippy]

Now that's a good question vapour barrier, somebody else may have to answer that, or ring your local council and ask to speak to a Building Control Officer and ask him/her they are very helpful.

Celotex aren't the only makers of solid insulation, their are others exactly the same but cheaper, also I have no idea about whether the total cost is expensive or not as I don't know the size of your loft.
If your buying a lot I would go online and get quotes from different suppliers for the whole lot, it may work out cheaper.

 

[Eddman]

I have spoken to a friendly local builder who assures me that 50mm celotex between the rafters and 32,5mm insulated plasterboard across the face of the rafters is sufficient insulation on the sloping ceiling part.
He evaded the question about what is needed in the knee wall! I was thinking of putting the same as in the sloping ceiling - any raise on that?...

Thanks Again

Eddy