Attic Insulation & Condensation Questions

Seth Brundle

We had the floor of our attic insulated with loft roll when we moved in about five years ago.
We've noticed condensation forming on the trusses and pitch overhead in the attic. Stuff placed in the attic gets damp.
I reckon that the existing insulation is working. Going up into the attic today, it was roasting when compared to the landing below it.

So, what is causing the condensation?
My guess is that the vents are possibly blocked but I'm no expert.
Not sure if this is due to some of the newer insulation blocking the vent holes or possibly due to the vent holes in the original soffit not lining up with the plastic soffits replaced subsequently. Possibly both.

Anyhow, we had an insulation guy come in last week when he was doing a job for a neighbour. He told us that he could spray a breathable foam between the trusses which somehow would solve our problems.

Does this form of insulation require an absence of ventilation in the attic (as I can't see how insulating the roof is of use if you've air flowing between the attic floor and roof)?
Would this breathable foam cure our condensation issues?
Would we be better off just making sure the vents are allowing enough air in & out and not bother with the foam?

BryanF

Assume you have Eaves vents in the soffit - Corrie board oversized and folded into the joists leaving about 50Mm gap for ventilation

Yellow_Fern

I am not expert but I dont see how spray foam will help anything. Concentrate on ensuring you have enough ventilation into the attic. If the soffits wont work, there are other simply enough options.

Seth Brundle

BryanF wrote: »

Assume you have Eaves vents in the soffit - Corrie board oversized and folded into the joists leaving about 50Mm gap for ventilation

That will insulate the roof. But will it resolve the condensation problems?
If I am incorrect and the ventialtion is ok up there, will insulating the roof be pointless?

Yellow_Fern wrote: »

I am not expert but I dont see how spray foam will help anything. Concentrate on ensuring you have enough ventilation into the attic. If the soffits wont work, there are other simply enough options.

I'm thinking along these lines.
I reckon that the vents in the PVC facia & soffits aren't lining up wiht the original vents in the timber soffits which is causing the problem.
There may be insulation pushed down towards the vents also which I'll pull back.
If I get the ventilation sorted up there, then my view is that we don't need any foam up there.

sydthebeat

Seth Brundle wrote: »

That will insulate the roof. But will it resolve the condensation problems?
If I am incorrect and the ventialtion is ok up there, will insulating the roof be pointless?
.

no... it wont insulate the roof, it will ventilate the roof
your issue is ventilation, not insulation

its not surprising an "insulation guy" proposed installing more insulation

Seth Brundle

Aah ok thanks - I was incorrectly thinking of something completely different.

So corrie board folded into the joists: am I correct in thinking now that this is to help prevent the existing insulation from blocking the vents like this?
Initially I had this vision of the board acting as another layer or something - this I now presume is incorrect and it is more of a baffle type thing (as per the link)?

As for the insulation guy upselling - hence my thread

sydthebeat

What Bryan is describing is more of a DIY version of this:

https://static.cmostores.com/uploads/products/2/l/sandtoft-eaves-vent-system-0w5ckguatg-g.jpg

just use the thickest corriboard you can, and slip down between the insulation and the felt.

another option that ive specified in similar cases is some 50mm white wavin pipes cut to size and slip 2 each between every rafter

Seth Brundle

Cool thanks.
Am I correct that these are only for a foot or two from the eaves into the attic (not all the way along) so that air can flow into the attic space unimpeeded?

sydthebeat

Seth Brundle wrote: »

Cool thanks.
Am I correct that these are only for a foot or two from the eaves into the attic (not all the way along) so that air can flow into the attic space unimpeeded?

exactly, its just to hold the insulation, that is on the ceiling, away from the felt

you could of course do it by pulling the insulation away, but you run the risk then of having less insulation on a notorious thermal bridge area, which cause condensation and eventual staining, mould etc.

better to pack the insulation in and down so that it covers the inner leaf and wall plate etc

BryanF

Only seeing this now - What syd said.