Boarding the loft room, should I double insulate?

glasgowdan

I've just pulled down all the old hardboard, polystyrene and wallpaper from my loft ceiling and am going to fit new plasterboard all over before building out a big storage cupboard. I'm just wondering if it's worth packing between the rafters with some kind of insulation to replace the fibreglass as well as fitting insulated plasterboard?

Also, what kind of order should things be done in? Board top down, bottom up? Board the angles in the corners first or last? I'm replacing the flat ceiling and the angled eaves, planning to keep the vertical walls to reduce work.

Any help would be great, I'm new to all this!

glasgowdan

bmthmark

You can get something called Celotex that you can cut and slot between the rafters. Not sure how much it costs though.

BoxerfanUK

Be careful, you are supposed to leave a 2" airgap between insulation and the underside of roof felt/tiling to prevent damp issues.

thebaldwindowfitter

As above rigid insulation is best i would have this 20mm less than depth of roof spar then vapour barrier . I would start boarding from the bottom and the biggest i could away from corners then carry on up staggering the joints

Grenage

I would use Celotex if I was having a warm loft; using foil tape across the joins. As said above, you'll want to leave a 2" gap between the felt and insulation, and ideally have it so air can flow between the eave and ridge vents (if you have them).

thebaldwindowfitter

Grenage wrote: »

I would use Celotex if I was having a warm loft; using foil tape across the joins. As said above, you'll want to leave a 2" gap between the felt and insulation, and ideally have it so air can flow between the eave and ridge vents (if you have them).

As such no gap is needed due to the roof being tongue and groved on the top surface with timber http://www.kingspaninsulation.co.uk/getattachment/7b661a05-8f84-47ac-a46c-42acd18f8576/Thermapitch-TP10-pdf.pdf

System

thebaldwindowfitter wrote: »

As such no gap is needed due to the roof being tongue and groved on the top surface with timber http://www.kingspaninsulation.co.uk/getattachment/7b661a05-8f84-47ac-a46c-42acd18f8576/Thermapitch-TP10-pdf.pdf

On a retrofit application it's always better to leave 50mm min air gap below the sarking boards unless you have replaced the felt with a breathable membrane or know the existing membrane is breathable...

Op you are looking some decent money to install rigid insulation and this type of insulation is rarely funded in any of the government schemes, best solution would be 50mm air gap, fill the rest of the depth of the rafter with celotex/kingspan/quinntherm then use an insulated plasterboard on the underside of the rafters... Just not too wallet friendly

glasgowdan

the_r_sole wrote: »

On a retrofit application it's always better to leave 50mm min air gap below the sarking boards unless you have replaced the felt with a breathable membrane or know the existing membrane is breathable...

Op you are looking some decent money to install rigid insulation and this type of insulation is rarely funded in any of the government schemes, best solution would be 50mm air gap, fill the rest of the depth of the rafter with celotex/kingspan/quinntherm then use an insulated plasterboard on the underside of the rafters... Just not too wallet friendly

Aye that's what I'm expecting, I'd rather it was all done properly.

The vertical wall hardboards are going to be left alone, and possibly just boarded over with plain plasterboard...any issues with this? It's just a time saver!

MX5huggy

I've done mine with Celotex (well done most of it) maintaining 50mm air gap (I don't have sarking boards only felt) mines double hipped like yours. Working upside down trying to tightly fit it in the space between the rafters right down to the eaves then using a expanding foam gun to fill the gaps was a nightmare. I then want to go over the whole lot again with another Layer of 75mm Celotex but the angles and junctions are putting me off getting on. If you've got the head height just put 150mm over the rafters if you can.

glasgowdan

I've priced this up and looks like £450 for the 70mm insulation and insulated 27mm plasterboards plus a bit for screws and tape. I've got some joinery to do first now as I've removed some old cupboards and need to reinstate the walls. The jobs list doesn't half grow arms and legs!

Cap off water supply to sink before removing sink and unit
Get an electrician to wire and place new lights and sockets
Joinery, sort area of missing floorboards and wall
Remove skirtings
Strip wallpaper
Fit insulation between rafters and tape
Remove nails from floor
Fit plasterboard
Tape and fill joints
Build partition wall for walk in storage
Fit new skirtings
Apply corner tape to edges of hardboard in certain areas
Paint skirtings
Apply lining paper and paint all ceilings and walls
Fit electrical components to walls/ceiling
Carpet fit in loft and stairway (full wallpapering and paint required through stairway too).

I'm starting to see this being a 2018 completion date job! Free days are in very short aupply