What insualtion to combat condensation?

two wheels good · 12-10-2011 11:39AM #1

I want to insulate the ceiling at the front door to combat the condensation which is quite heavy.
The ceiling is formed by one end of a concrete slab that also forms the roof of the porch outside - hence the cold temperature at the hall ceiling.

I had thought that a thin sheet of aeroboard covered by 6mm plywood or MDF would do. But it seems aeroboard sheets aren't easy to find. Maybe aluminium foil based insulation is better?

Please could some expert recommend the best approach - what type of insulation and if an air-gap is necessary between insulation and ceiling?

Thanks

MicktheMan · 12-10-2011 04:08PM

From your description it seems you have a continuous concrete slab, part of which is outside the thermal envelope (porch).
If this is true and you already have visable condensation forming within the thermal envelope (hall ceiling) then insulating this internal ceiling may well make matters worse.
Without seeing the problem it is difficult to advise but the proper solution may involve insulating the part of the slab outside the thermal envelope (above and below) as well as possibly reducing the relative humidity within the thermal envelope (living space).

BryanF · 12-10-2011 06:52PM

two wheels good wrote: »

I want to insulate the ceiling at the front door to combat the condensation which is quite heavy.
The ceiling is formed by one end of a concrete slab that also forms the roof of the porch outside - hence the cold temperature at the hall ceiling.

I had thought that a thin sheet of aeroboard covered by 6mm plywood or MDF would do. But it seems aeroboard sheets aren't easy to find. Maybe aluminium foil based insulation is better?

Please could some expert recommend the best approach - what type of insulation and if an air-gap is necessary between insulation and ceiling?

Thanks

would this the semi-d type concrete flat roof over entrance job? i surveyed one recently which had the same problem.
as Mick said, external insulation is the only way to go.. internal solutions will only cause more headaches in long term..

two wheels good · 12-10-2011 09:12PM

Thanks for the advice. Yes, a concrete slab forms the porch roof and extends into the hall.
It didn't occur to me to insulate it outside. What's suitable? Is there something weatherproof?

I'd seen aeroboard lining damp walls in the (distant) past. My plan was to try to stop warm air reaching the cold surface in the hall.

BryanF · 12-10-2011 10:16PM

think of it like this: the underside of the concrete is a cold surface that causes moisture to condense on it. so if you insulate beneath that cold concrete surface your are in a affect just hiding the problem, moisture can still migrate to it and condense..

I've seen really nice porches/ canopy porch coverings lately. mainly done in a standing seam zinc (or similar cheaper option) *please note external alterations may require planning (if you throw up some pic's once you decide what your doing you probably get a better idea)

A HD EPS insulation is prob the cheapest option but i prefer a rigid wood fibre or rigid mineral wool product as their low on embodied energy and easer to recycle/dispose of.

I appreciate cost is an issue for most at the moment but i would guess that all your walls could do with insulation and I would recommend EWI over dryling for the same reason outlined above.

heinbloed · 13-10-2011 08:21AM

External insulation won't help, the two previous advisers are wrong.
A "thermal separation" is the only passive answer. Meaning a gap between warm house and cold slab has to be created.

The reason is simple: the slab is not heated, it is exposed with 5 sides to the outside temperature and with 1 side to the internal structure. Which the slab cools down to the condensation point.

An ice cube doesn't get warm if wrapping insulation around it.

Since this is a faulty design the builder is responsible. A clear contravention of building regulations.

Get a civil engineer to simulate the situation, wufi would be the right tool for this.But one can use logic as well.

No matter how much insulation material is added externally the problem will stay. One can't heat an external concrete slab with a strip of 20 degrees Celsius , the room temperature of the hall.

Another technical solution would be to isolate the slab from internal moisture impact and heat the room-facing surface of the slab, for example with an electric resistance heating strip. Like the ones used for frost protecting water pipes. This would demand 24 hour heating and a perfect sealing.
Nothing for DIYers.

BryanF · 13-10-2011 09:16AM

heinbloed wrote: »

External insulation won't help, the two previous advisers are wrong.
A "thermal separation" is the only passive answer. Meaning a gap between warm house and cold slab has to be created.

The reason is simple: the slab is not heated, it is exposed with 5 sides to the outside temperature and with 1 side to the internal structure. Which the slab cools down to the condensation point.

An ice cube doesn't get warm if wrapping insulation around it.

Since this is a faulty design the builder is responsible. A clear contravention of building regulations.

Get a civil engineer to simulate the situation, wufi would be the right tool for this.But one can use logic as well.

No matter how much insulation material is added externally the problem will stay. One can't heat an external concrete slab with a strip of 20 degrees Celsius , the room temperature of the hall.

Another technical solution would be to isolate the slab from internal moisture impact and heat the room-facing surface of the slab, for example with an electric resistance heating strip. Like the ones used for frost protecting water pipes. This would demand 24 hour heating and a perfect sealing.
Nothing for DIYers.

heinbloed,
well long time no here,
hold on a minute there.. we are talking about a flat conc roof of an existing house probably pre 80's if not 50's!! what are you talking about

relax on the engineer with someone to sue solution

as regards your ice cube?

lets just say its a cold concrete flat roof and by insulating it external on all sides but the internal ceiling you are warming the slab and keeping the interstitial condensation/ due point to the outside of the structure. or you could go (as i suggested above) with a more breathable insulation and metal cladding/roofing which could incorporate your air gap

I do agree, "maybe not for DIY'ers" but that depends on the OP

heinbloed · 13-10-2011 09:25AM

Less words and more professionalism, BrianF.

The OP wrote:

The ceiling is formed by one end of a concrete slab that also forms the roof of the porch outside - hence the cold temperature at the hall ceiling.

The situation is clear: A six sided element (a cubistic element) is showing condensation at it's only warm side.

Thermal insulation of the 5 exposed sides does not take away 'the cold', the dew point would only be moved by a cm or two outwards. The problem not solved.

The laws of physics haven't changed.

BryanF · 13-10-2011 10:07AM

yes the laws of physic's don't change:D

there's nothing to say the external canopy/porch cannot be wrapped..

two wheels good wrote: »

concrete slab forms the porch roof and extends into the hall.

and it can be done to an good visual standard also:

thats why i said:

BryanF wrote: »

by insulating it external on all sides
.....
I've seen really nice porches/ canopy porch coverings lately. mainly done in a standing seam zinc (or similar cheaper option) *please note external alterations may require planning (if you throw up some pic's once you decide what your doing you probably get a better idea)

and also discussed the rest of the walls needing insulation...

What insualtion to combat condensation?

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