Drafts Between Ceiling and Floor

[DrewB]

As I've mentioned perviously I have an Edwardian stone walled property. There is the necassary gap between the internal lath and plaster and the outer stone walls but that is not my current concern. My concern is the gap between the ground floor ceiling and the floor above. This gap is partially filled with a suspended ash layer but has a void below the ash layer which extends right across the house and is open to the 'cavity' behind the lath and plaster. Thus any heat lost though the ground floor ceiling escapes into the 'cavity'. Worse still, if there is a wind outside there is a draft through that void.

I'm thinking it makes sense to try to block the void at the floor ends to reduce the drafts from the gap behind the lath and plaster. But am I right in thinking that minimising the air flow above the ceiling should not cause any damp issues since there should not be any damp in either the ceiling or floor above (unless my daughter floods the shower again ) and the rooms should be at similar temperatures.
Can anyone see any other issues with reducing that air flow?

Would expanding foam be an appropriate material to use or is there a better alternative, remembering that access is not easy and the gap is irregular?

Any thought would be most welcome.

Drew

 

[Moo]

heat lost though the ground floor ceiling

I'm sure that I'm just being dim again, but I don't understand how that can happen, unless you've got holes in your ceiling.

 

[DrewB]

Moo,
The heat loss is by conduction through the lath and plaster ceiling into the void then by convection out into the 'cavity' between the outer stone wall and the lath and plaster inner wall and hence into the loft space.
Unfortunately plaster is not a very good insulator and since the warmest part of the ground floor rooms is inevitably just below the ceiling, there is definately loss throught the ceiling. Its just the same as from the upper floor into the loft space. Except that unfortunately I can't add 200mm of insulation between the ground floor ceiling and the first floor floor boards. But hopefully I can contain the warm air rather than have it escaping into the atmosphere.

Drew.

 

[MdB]

In my inexpert view it sounds like a good idea to seal the void at the floor ends.

 

[AMc]

It's hard to visualise the gap - can you take a picture?

Sealing the gap sounds like a good idea - heat loss between floors with solid walls is a very common issue with period houses as the joists sit into the external wall and there are always small gaps in the pointing for air to blow through. If your carpet upstairs gets dirty around the very edges its because heat escaping upwards causes draughts sucking in cold, dirty air in from outside with the carpet acting like a hoover bag - yuk.

IMHO It shouldn't cause damp issues unless you have serious problems with penetrating moisture or leaks above, both of which are more important to deal with!

I'm not a fan of expanding foam despite it being used a fair bit in my house and by my hand - it's a beggar to control and has a nasty habit of going just where you don't want it to blocking access to where you do. On the other hand it is cheap,, permanent & reasonably reversible.
I thought about stuffing glass fibre insulation (or wool if you're feeling rich) but there is the potential for it to get blown around if you have to chop it up small to get it into the gap.
I would probably - reluctantly - use the foam. If you've not used it before try and be careful to avoid overstuffing. It continues to expand for a while and inexperienced builders have literally popped plasterboard off the wall sealing small gaps with too much foam!

Screwfix do cheap cans of foam. My builders considered the stuff with a disposable spout to be less hassle than the stuff that needs an applicator (get gunged up easily). Don't expect to use half and can then come back to it later - I've never managed to get a part used can to work again so plan before you start squirting.

Good luck!