dormer walls

[dormermike]

The front bedroom in our dormer bungalow is getting colder than thee rest of the upstairs rooms. I think this is because its south facing and more exposed. There is also an almighty draft blowing through the eaves, which i think is blowing the warmth out of the insulation on the walls.

Walls are attic insulation 100mm covered with a vapour barrier.

Ceiling (sloped) is insulation board.

Roof (attic) is 100mm. Attic here is unreachable.

The walls feel cold to touch in the mornings.

I am considering adding insulation board in the eaves crawl space (1.2m height) to bolster the insulation and perhaps reduce the draft effect.

Does this sound sensible? Ive managed to reduce the gale that was blowing in the floor space (gap with downstair ceiling).

Thanks
Mike

 

[dormermike]

Any ideas out there?

 

[dormermike]

Nobody have any ideas on this?

I have a infrared thermometer and have identified several cold spots on the walls and ceilings.. was only 20 quid and is great. I will improve the insulation in those areas first.

 

[freddiemercurystwin]

You need to add insulation, if there is no access to areas you will need to make an access with either a hole that you then seal up or an insulated hatch. Your post is not particularly clear tbh which is maybe why you've had no response. Is this a room in the roof? any chance of you drawing a rudimentary section?

 

[dormermike]

You need to add insulation, if there is no access to areas you will need to make an access with either a hole that you then seal up or an insulated hatch. Your post is not particularly clear tbh which is maybe why you've had no response. Is this a room in the roof? any chance of you drawing a rudimentary section?

Thanks for the reply and sorry about the vague post.

I have attached an image (my paint skills are not great either).

Untitled

• dormermike
• 9 Jan 2012
• 1

Basically, the lines in red represent existing insulation - it is the rockwool / loft insulation stuff and is 100mm. In the walls this insulation is held in place using a sheet of what I guess is a membrane of some sort.

I am considering "boxing in" this insulation using insulation board, from the eaves side, shown in blue. The walls at the moment are cold as the ventilation in the eaves is very good, but it blows the heat out of the existing insulation.

The "attic" has cold spots also (confirmed with a IR thermometer) but I will need to cut an access way as the hatch is about 15m and the crawlspace is tiny.

EDIT: The box inside the triangle in my rather excellent diagram is in fact a upstairs bedroom - its also rather big, south facing, and tends to get hot in summer and coldish in winter. Existing insulation is not too bad, but where we are situated on a bend in a road the corner of the house tends to get a blast of wind, which i think is making the upstairs bedroom walls cold.

 

[dormermike]

For the eaves side of the dormer/attic room wall insulation as there is lots of room i'm considering Kingspan K7 100mm.

This would mean the wall construction is as follows:

Plasterboard -> 100mm rockwool > 100mm Kingspan k7

For the actual dormer part of the room, i'm going to rip down the ceiling and walls and install kingspan k7 and then reinstall plasterboard on top.

Does all this sound ok?

 

[freddiemercurystwin]

will post later

 

[freddiemercurystwin]

Yes your plans sound largely OK.

Do you know if you have felt beneath your tiles or not? In a proper loft conversion or a new build if you had felt you would need to ensure you maintained a ventilation gap of 50mm between the insulation and the underside of the felt. This cavity would be vented at the bottom of the pitch at the eaves and at the top at the ridge. If the roof is felted do you know if you have any existing ventilation at the ridge or eaves?

If there is felt and no ventilation at the ridge or eaves you should consider adding adequate ventilation when you do your insulation.

In order to achieve the 50mm air gap (headroom permitting) it is usually necessary to add as much insulation between the rafters as you can and then a continuous layer of insulation across the underside of the existing rafters and then foil backed plasterboard. Overall it would be sensible to aim at about 100-125mm of K7.

The images I posted in this thread may be of use //www.diynot.com/forums/floors...-dormer-conversion-need-advice-please.307269/

 

[dormermike]

Thanks for the reply!

Yes the roof tiles have a felt backing, the construction is currently:

Plasterboard, 50mm insulation board*, air gap approx 50mm, felt, concrete tile

*foil backed, not sure what it is

There is a single vent at the top of each side of the roof near the ridge.

The eaves area is very windy, the soffit vents are continuous around the entire building, but have been blocked with insulation in some areas - there is no condensation or anything like that, and it still blows a gale so it blocking them hasn't been detrimental i think.

This was all built in 1994 btw, if that matters. Not sure what standards were in place then.

 

[freddiemercurystwin]

So you say you have 50mm insulation between the existing rafters, if you want a warmer room then adding a layer of say 50-75mm beneath the existing rafters and then new plasterboard would be sensible.

It sounds like the ventilation you have already is working Ok, it would be prudent to makes sure any existing ventilation is not blocked by insulation. If your new insulation is done correctly then clearing the ventilation ways should not have any adverse effects on the rooms in terms of increasing draughts or losing heat.

Seal any gaps between the insulation and wonky rafters etc with expanding foam.

Foil backed plasterboard is normal plasterboard with a foil facing on the rear face, this acts as a barrier to prevent any moisture getting beyond the plasterboard ann condensing in the insulation. It cost very little more than normal plasterboard.

 

[dormermike]

So you say you have 50mm insulation between the existing rafters, if you want a warmer room then adding a layer of say 50-75mm beneath the existing rafters and then new plasterboard would be sensible.

It sounds like the ventilation you have already is working Ok, it would be prudent to makes sure any existing ventilation is not blocked by insulation. If your new insulation is done correctly then clearing the ventilation ways should not have any adverse effects on the rooms in terms of increasing draughts or losing heat.

Seal any gaps between the insulation and wonky rafters etc with expanding foam.

Foil backed plasterboard is normal plasterboard with a foil facing on the rear face, this acts as a barrier to prevent any moisture getting beyond the plasterboard ann condensing in the insulation. It cost very little more than normal plasterboard.

Good idea on that - i was going to remove the existing 50mm foil backed insulation board and replace with 100mm k7, but actually it makes much more sense to board 50mm k7 over the existing 50mm!! Doh

Thanks again for your help, much appreciated.