Fibreglass vs Kingspan type Panels for Attic Insulation

championc

Hi all,

I have my attic fibreglassed with about 4" Moy stuff which I did about 15 years or so ago. I am considering Dumping it and replacing the whole lot with Kingspan type panels (like the K7). I don't mind if the investment takes 5 or 10 years to replay itself but my main question is as to how much better insulation is provided by the Panels over traditional Fibreglass. I also wonder what the difference is between 100mm vs 200mm depth panels in.


Regards
C

10-10-20

If you are thinking of placing these Kingspan solid panels between the joists or rafters, think again.
They are hard to cut straight, difficult to install and a pain to seal.
You really need to think about placing a second layer of panels over them, lapping the first, to achieve any sort of a seal.
Go with fiberglass or even a green product such Warmcel.

wazzoraybelle

You might consider rockwool flexi which would fit tight between the joists.
Personally I'd just top up the fibreglass you have with more.

getfit

The basic rule of thumb I was given is that a kingspan board is three times as insulating as fibreglass. So 300mm of fibreglass is about equal to a 100mm board. The lads are right boards are very hard to get right. If you have the space i'd keep the 100mm you have there already and then throw on as much fibreglass as you can. If you could put 150mm + 150mm on top of the 100m, giving you a total of 400mm, you'd be doing very well - and it would be cheaper and easier than kingspan boards...

championc

My plan is to lay panels at right angles to the joists and then a floor on top (I currently have it floored and is easy to take up). Given that I have a trussed roof, there isn't a huge depth in the joists and the fibreglass uses up that height, it would be nearly impossible for me to lay fibreglass and then have a floor raised above this. However, panels are ideal to lay a floor directly on top of since the weight will be distributed.

So with my 4" of fibreglass, would I be wasting my time on 200mm of panels and so just stay with 100mm. Would 100mm panels be the equivalent to 200mm of fibreglass ?


C

hopalong_ie

With the Polyiso Panels such as Xtratherm Rafterloc (K7) its 3 times more insulating. 100mm of the Panels = 300mm of Fibreglass. 50mm of Panel = 150mm of Fibreglass. I personally plan to install 100mm (Rafterloc as described below) in my ceiling and possibly 200mm in the eves where its of limited storage use. Take your time and you will get good results. Have also seen people use 400mm wide rafterloc. Split one into two 200mm and you now have 600mm of compressable board for your ceiling. Rafter loc has 20 - 30mm of play per sheet.

championc

Thanks hopalong

Would you recommend that I remove all the old Fibreglass and cut and run the panels between the joists ? If I was to lay the Panels over the top of everything, I would have a small air gap but could I still have possible condensation ?


C

luap_42

championc wrote: »

Would you recommend that I remove all the old Fibreglass and cut and run the panels between the joists ? If I was to lay the Panels over the top of everything, I would have a small air gap but could I still have possible condensation ?C

About to do just this in my detached bungalow with W trusses, in order to lay flooring down the centre section.

I've removed the cross layed fibre glass from the centre section and it's going out under the outer sides of the trusses, which will increase that fibre glass to 12" and is above the bedrooms, living room, kitchen, utility & bathroom. So I am then left with fairly new fibre glass in between 4" joists in the centre section.

The plan is to lay 1" thick battens across the centre section joists in three parallel runs that run the full length of the centre section and two 2" thick vertcial edge runs on each side parallel to the 1" battens. Effectively building a barebones frame to box in Kingspan K7 Kooltherm 50mm boards. I'll have to cut the Kingspan down the middle to get them up the loft hatch, but I'll lay the two cut pieces back together once up and they should be fairly tight together.

Once the kingspan is in it's box, I'm planning to just lay 8'x2' chipboard flooring on top, and if it's moving then 2 widgets per exposed 8' chipboard edge to keep the boards in place.

There'll be a 6" gap at each side of the K7/floor box, which I'll just refill with fibre glass to prevent upward heat there. The centre section will then have 4" fibre glass between joists and 2" Kingspan Kooltherm K7 (equivalent to 6" fibre glass) on top, or 10" fibre glass equivalent. This is all above a hallway and part of the living room.

I'm hoping that the 1" thick battens under the Kingspan will suffice as an air gap to prevent condensation on the joists and allow whatever electrical cables to run across the centre section (after I get an electrician to tidy that up first!).

Anyway, I think this is a relatively good plan to allow me to floor my attic for storage of little used items, while maintaining the insulation and avoiding condensation and deterioration of electrical cables.

Any comments or ideas?

Carlow52

what u have is
4" gf
1" airgap
2" ks

If the 1" air gap is ventilated, then the 2" ks is meaningless.

If the gap is not ventilated then the ks will act as an impermeable membrane and the moisture that passes through the gf will be captured.

luap_42

Carlow52 wrote: »

what u have is
4" gf
1" airgap
2" ks

If the 1" air gap is ventilated, then the 2" ks is meaningless.

If the gap is not ventilated then the ks will act as an impermeable membrane and the moisture that passes through the gf will be captured.

The 1" air gap is only where the kingspan is laid, which is most of the centre section of the house, above mostly 25' long hallway and 10' section of living room. It will be surrounded by an area of cross-layed fibre glass directly on the joists. So it will be effectively unventilated due to the surrounding fibre glass and cross-layed battens (required for routing electric cables) that the kingspan is laid on. The hallway will have very little condensation produced, and all wet rooms are on the sides of the house and will have only fibre glass insulation above them. The attic above all insulation is ventilated.

Regarding condensation, I'm going to install a heat recovery system to provide/extract air to the house, so I'm thinking that the majority of condensation that would naturally evaporate up into the attic will be extracted by the heat recovery system.

Carlow52

Thanks for the answer,

Just on the water laden air. There is a myth around that water laden air in an absolutely still house will not move throughout the house.

This is wrong as water laden air has a higher partial vapour pressure than air with less water in it so the air will migrate to equalise the vapour pressure. A bit like the way a drop of dye will spread out in a glass of water.
In addition warm air will migrate towards colder air, hence u get condensation on external walls in cold rooms, typically behind presses



ps for water read moisture

Arddon

would using insulated plasterboards on your ceilings do the same trick (to an extent) as using fibreglass/K7???

Graaaaa

If you're laying boards in the attic, then maybe consider insulating at rafter level and having a warm attic space instead of a cold one?
I agree that cutting the boards to fit between the rafters is difficult, although I haven't tried it myself yet. I am still looking into it and came across a sheepwool matress. The supplier suggests packing this between rafters and holding it in by fixing chicken wire to the rafters after. Rolls come in various widths, thicknesses and lengths. The cliams about being naturally moisture resistant and breathing with the timbers is interesting. Also the sustainable sources from Wales and Connemara.
Costwise it seems about 3 times that of a roll of loft insulation from the big popular hardware stores.
Anybody have any experience?
www.blackmountaininsulation.com

luap_42

Graaaaa wrote: »

If you're laying boards in the attic, then maybe consider insulating at rafter level and having a warm attic space instead of a cold one?
I agree that cutting the boards to fit between the rafters is difficult, although I haven't tried it myself yet. I am still looking into it and came across a sheepwool matress. The supplier suggests packing this between rafters and holding it in by fixing chicken wire to the rafters after. Rolls come in various widths, thicknesses and lengths. The cliams about being naturally moisture resistant and breathing with the timbers is interesting. Also the sustainable sources from Wales and Connemara.
Costwise it seems about 3 times that of a roll of loft insulation from the big popular hardware stores.
Anybody have any experience?
www.blackmountaininsulation.com

Thanks, I'd thought about it, but I have no reason to heat the attic, it's just a waste of energy, so the attic is going to stay ventilated and cold with attic joists level insulation keeping heat in the rooms. I was thinking about kingspan between joists, but since I have fibreglass there already and have to cross lay something anyway, I'm going for the K7 and will endeavour to prevent moisture buildup in that space.

Carlow52: Thanks again. I agree about moisture movement, but there will still be less moisture in a hallway than in the lived in rooms, wet rooms, kitchen, and bedrooms.