Ideas on Retro-insulating the roofs of existing dwellings

ircoha

The purpose of this thread is to explore how best to address the task of "retro-insulating" the roofs of existing dwellings.

As an example, I live in a converted dormer so very little of the roof space is visible from the residual attic space.

I want to increase the amount of insulation on the roof so I am considering taking off the roof tiles and ......[then what?]

Anyone any thoughts, or is this a post for after hours?:)

I have 2 chimneys and 8 velux windows

There was much today at the building show about making dwellings airtight.

If I do strip off the roof tiles is it worth making the roof airtight for a heat recovery system and then counter batten before putting back the roof tiles.

What else would you do with the roof off.

Do u think planning is required?

Thanks in advance.

CJhaughey

Could you strip the existing tiles and felt.
1, Add wooden sarking outside the rafters.
2, Felt and counterbatten roof then batten for whatever roof covering is then going to be fitted.
3, inside the rafters nail 2x1 s in the corner of the sarking/rafter joint and also in the centre of the span between rafters then fix hardboard to the 2x1s running down to the wall plate, this will allow free movement of air to keep your roof dry.
4,On the inside of the rafter fix appropriate size timber to make a deeper rafter this will be your insulation cavity.
5, Fix polyethylene vapour barrier to inside of rafters and across apex of ceiling.
6,Slab or fit T+G to the ceiling.
Pump in blown cellulose insulation to desired depth.

Just to note, Velux windows are a net loss of energy, the seal between roof and window frame is hard to insulate properly.

I have HRV and it is a fantastic system, put the cooker on and know that you aren't wasting heat.
Our last ESB bill was 52 euro

ircoha

CJhaughey wrote:

Could you strip the existing tiles and felt.
1, Add wooden sarking outside the rafters.
2, Felt and counterbatten roof then batten for whatever roof covering is then going to be fitted.
3, inside the rafters nail 2x1 s in the corner of the sarking/rafter joint and also in the centre of the span between rafters then fix hardboard to the 2x1s running down to the wall plate, this will allow free movement of air to keep your roof dry.
4,On the inside of the rafter fix appropriate size timber to make a deeper rafter this will be your insulation cavity.
5, Fix polyethylene vapour barrier to inside of rafters and across apex of ceiling.
6,Slab or fit T+G to the ceiling.
Pump in blown cellulose insulation to desired depth.

Just to note, Velux windows are a net loss of energy, the seal between roof and window frame is hard to insulate properly.

I have HRV and it is a fantastic system, put the cooker on and know that you aren't wasting heat.
Our last ESB bill was 52 euro

Thanks CJH, one prob I have is that the dormer is converted so any deepening of the rafter will be have to be done from the outside.

Was ur HRV an original or retrofitted, pls pm me with the make pls.

I saw a house recently being finished and the roof is sheet metal on the rafters with the ridge and hip joints flashed and sealed with expanded foam, and then battened/counter battened.

Any thoughts on how it breaths?

ardara1

Hi Folks -

Putting insulation over the rafters creates a WARM ROOF - basically keeping the roof timbers at a stable temperture close to that of the inside temp.
Fixing the system causes the real problem. Roofs act like aircraft wing actually being sucked off the building by lower pressures above created by wind - therefore your fixings are critical.
You'll need a counter batten over the insulation layer covering the rafters - notmally 40mm, this is fixed using helical fixings normally 8/m2 depending on exposure/pitch & roof tile weight. They're expensive, normally 23c a piece.
You will have to put a breather membrane over the c battens then tile and slate as normal into the c batten.
It important as with all brathers that you put a vapour control layer to the inner face of the construction.
Insulation - 60 between and 60 over ht erafters - PIR foil faced type to achieve u-value of 0.20
SEE BRE paper GBG 37 WARM ROOF for guidance.
The amount of cellulose you'll need to meet the same U-value will not fit into your rafter depth. Air tightness is important - but within the building as a whole sealing your roof when your floor is leaking still leads to a leaky home.

ircoha

I am obliged to ardara1 for this link

http://www.webdynamics.co.uk/

which is also in a similar post in gardening/DIY

http://www.boards.ie/vbulletin/showthread.php?p=52062864#post52062864