Insulation - Opinions

godtabh

House needs new insulation.

Got a few people in to give quotes

1. One lad has suggested rolling insulation on the floor, up the rafters around the living space and spray foaming the rafters around the attic. The logic of spray foaming the rafters around the attic is to stop drafts coming in.
   
2. One lad said to put insulation down on the floor and up the rafters and thats it
   
3. One lad said put insulation down on the floor and spray foam the rafters around the living space.
   

A big range of costs involved. What is the best way to insulate an attic?

Gumbo

Have you got a section through the attic space showing the thermal envelope proposed?
Habitable rooms?
Storage?
Whats under the floor etc

godtabh

Hopefully this makes sense

MicktheMan

godtabh wrote: »

House needs new insulation.

And you know this how?

Have you considered that perhaps your house (dormer) might benefit from air tightening works more than extra insulation?

These are the steps I reckon you should be following;
1. Decide on & define your thermal envelope. This is critical.
2. Test this thermal envelope for heat loss and determine which type of heat loss mechanism dominates
3. Decide how best to tackle the dominant weakness(es)
4. Have necessary remedial work done by competent tradesman (or perhaps do it yourself if so inclined).


Fyi, I wouldn't let any of those 3 'lads' near my dogs house never mind my attic. Also, spray foaming rafters does not make them airtight.

godtabh

MicktheMan wrote: »

And you know this how?

The house has had all its Insullation in the attic taken out.

Gumbo

godtabh wrote: »

Hopefully this makes sense

Define the Thermal envelope.
Joist Insulation (The Green Line) will be fighting against the rafter and dormer Insulation (Purple Line). Like creating an envelope within an envelope.

Air tightness measures will be crucial here as with any timber/dormer construction.

MicktheMan

godtabh wrote: »

The house has had all its Insullation in the attic taken out.

Ha, well that's a good answer.:D

The reason I asked is that more often than not, in dormers, you can spend a fortune adding insulation with little return when the primary mechanism for heat loss is air leakage and not lack of insulation.

My other points are still valid.

godtabh

Spoke to another insulation company. He says to spray the external envelope of the attic and that should seal it/keep drafts out. I assume that would go a long way for air tightens up there.