Wood fibre boards between lower part of rafters, daft idea?

[Jblakes]

Morning all,

So all the rooms upstairs are now boarded/plastered and decorated. The loft has had insulation put down, so a massive difference to warmth upstairs.

The issue we are having is, our ceiling upstairs are sort of angled at the edges and due to the air flow gaps (and general old roof, now felt), these are cold spots and keep being sort of damp and need wiping. Would attaching wood fibre boards between the rafters for only the lower, outer egde region solve this issue, they are breathable so I assume allow moisture/air through them?. The roof is baltic due to drafts, so can't see this causing a ventilation issue. My old concern is would they become rotten over time, due to the cold air, moisture etc.

What are your thoughts

Kind regards

James

 

[Lacan07]

What you're experiencing is the warm, moist air condensing when it settles on those cold spots so yes some kind of insulation between the rafters would help mitigate this. You can use wood fibre products, something like Steicoflex would be ideal as its flexible and provides a friction fit. Just cut it slightly larger than the width of the rafters. I think you'll need to leave a 50mm gap for ventilation between the insulation and the roof felt if its the old style bitumen and 20mm if its the modern breathable fabric type. (double check those figures). So if your rafters are 90mm deep (like mine) you use 40mm insulation if bitumen, etc.

 

[Jblakes]

Well our roof is that old it doesnt have a felt underlay bit .

I will try and see if I can fit boards down to the bottom of the rafters and hope it sorts the issues.

Kind regards
James

 

[malcolm]

Photos would be useful to clarify the question.

My attic room has a sloped ceiling and I insulated between the rafters. It's important to have a 50mm or so air gap between the insulation and the roof for ventilation.

 

[Jblakes]

This is only one I have, child asleep in it at min.

Anyway you can see the hole in the ceiling have a slope, all along this the paint sort of sticky to too touch, I assume it like suggested cold/hot air causing this. Hope this clears up the problem.

Kind regard
James

 

[fernicarry]

Should be straightforward to continue your loft insulation down that short section and onto the wall head. Ensure there is space above to ventilate the back of the tiles or slates. Is it just the short sloping section that has this problem?

The upstairs rooms here have a good 5 feet or so of sloped ceiling so I can only get insulation into the first foot or so without ripping the plaster off. The flat area has the full regulation 300mm of insulation. At the moment the room I'm in has a temperature difference of 4 degrees between flat ceiling and outside wall with the sloping ceiling somewhere in the middle. The bathroom which does have insulation in the sloping area and in the studwork against the outside wall shows no temperature difference.

I never have any condensation on the internal walls but that could be the ventilation value of sliding sashes.

 

[Jblakes]

Yeah it's only that slope section that has the issue, I want sure if I could just push insulation down the gap or that would cause damp issues.

 

[Lacan07]

Yeah it's only that slope section that has the issue, I want sure if I could just push insulation down the gap or that would cause damp issues.

For a pitch that small I would just push the insulation in from above if you can - job done.

 

[Jblakes]

Gonna be a tight squeeze

 

[fernicarry]

If there isn't much room above the slope then you won't get much added insulation value so the problem may persist.

How about adding some insulation on the lower face to get it up to a similar value of what you have in the loft? You'll lose a tiny bit off the corner but that shouldn't matter.

 

[Jblakes]

I'm not sure what depth is above the slope tbh, because it a very old house part of the support of the roof is a massive horizontal log, that kinda hinders getting to the slope.

Ill have a look at insulation underside, and see if it's an option

 

[Lacan07]

Fernicarry's idea is a good one, insulate from the inside.

 

[Jblakes]

How easy is it to do it?

 

[Lacan07]

I'm not sure what depth is above the slope tbh, because it a very old house part of the support of the roof is a massive horizontal log, that kinda hinders getting to the slope.

Ill have a look at insulation underside, and see if it's an option

Surely that pitch will be the depth of a rafter? The lath and plaster that creates the slope has to be attached to something.

Have the rafters in the loft been lath and plastered too? They are mine which is what would make it awkward to insulate from above.

 

[Lacan07]

How easy is it to do it?

Well you can either rip out the lath and plaster and insulate between the rafters (and on top if you wish).

Or you can just go straight on top as long as you can find the rafters for fixings. Take a rough measurement of the angle of the pitch to the ceiling (can use a bit of old wire for this if you don't have anything else) and use this to cut the edge of the insulation. You don't need to be major accurate, just to accommodate the slope top and bottom. Fill any gap top and bottom with expandable foam or similar.