Questions regarding insulation

rondeco

I'm currently in the middle of an attic conversion and its gone really well so far. The only thing I have to look after is the insulation.

It was recommended to me to use kingspan by the guy who did the basic conversion for me. Now, I have cut the sheets and fitted them in between the rafters and its worked out well, keeping a large gap to the felt. I used 30mm sheets. My question is does the sheeting need to be bound to the rafters or is it enought to just 'shove' it into the gaps between rafters?

And for the small gaps that invitably appear, what will I fill them in with? Some sort of expanding foam? Any help is greatly appreciated!

Viking House

rondeco wrote:

It was recommended to me to use kingspan by the guy who did the basic conversion for me. Now, I have cut the sheets and fitt them in between the rafters and its worked out well, keeping a large gap to the felt. I used 30mm sheets. My question is does the sheeting need to be bound to the rafters or is it enought to just 'shove' it into the gaps between rafters?
And for the small gaps that invitably appear, what will I fill them in with? Some sort of expanding foam? Any help is greatly appreciated!

You are creating a non-breathable roof there leaving the rafters as the only escape route for moisture leading to a build up of moisture in the wood. I would have preferred a more breathable safer solution. You can put a vapour control layer internally but it is extremly hard to get it airtight.

The U-value in Polyeurethene is not stable and is dependant on trapped gas which migrates leaving a worse U-value. Try holding a match beside a broken piece of new and old Kingspan and you will see the gas ignite in the fresh product and the older material has no effect on the flame.

Polyeurethene is only 22kgs/m3 and is too lightweight to prevent summer overheating in your attic. It also has the effect of loosing heat quickly similar to the way your caravan gets like an oven an hour after the sun comes out.

Lightweight insulations are for foundations and heavy insulations for the roof and walls.

Sorry for the news but its the truth!

10-10-20

rondeco, I have that Kingspan Thermaboard in my attic and it's the bain of my life.
The installer shoved the cut boards into the rafters willy-nilly and over half didn't fit correctly and subsequently fell out. Complete nightmare. (It was before I bought the house...)

So, I started trying to recover the situation and found out that kingspan actually recommend that a further insulation sheet be fitted perpendicular to the rafters to retain the boards and provide further insulation and air tightness. It all seems like a poorly worked out design in my mind.
You can either use more 30mm Thermaboard or drop down to 25mm.

B&Q prices for this work out at €7.75/m-sq for the 30mm, or €7.11/m-sq for the 25mm. Ex VAT.

10-10-20

Oh, and in relation to Viking-House's comments, he's correct in saying that this is a non-breathable setup, so you've got to have breathable sarking and felt on the roof. Otherwise you'll rot the timbers over time.
Have a look at the (confusing) Kingspan website and pull down the .PDF's for the Thermaboard products. They provide examples of install situations for all methods of application. It's a good guide!

Here...
http://www.insulation.kingspan.com/ireland/k7.htm
See Product and Applications Details.

rondeco

Thanks Guys for your input. What advice would you give me now? Should I just take it all out? Can I ask 10-10-20, how is causing you so much trouble?

10-10-20

No, no. Not at all!
Insulation is insulation at the end of the day. Just follow the Kingspan product brief and adapt your situation.
You'll also need to check that you have vents on the soffits which will supply air into the gap between the Kingspan and the roof-felt. This will regulate the trapped moisture.

My situation is that all of these boards (I'm not joking - 70%) fell out from between the rafters because they are a poor fit (a failing of the installer) and it's a pig of a job to have to refit each one and hold it in place. I'm using rolls of seam-tape stapled onto the beams. I must upload photos of some of my DIY work one day!

rondeco

10-10-20 wrote:

No, no. Not at all!
Insulation is insulation at the end of the day. Just follow the Kingspan product brief and adapt your situation.
You'll also need to check that you have vents on the soffits which will supply air into the gap between the Kingspan and the roof-felt. This will regulate the trapped moisture.

My situation is that all of these boards (I'm not joking - 70%) fell out from between the rafters because they are a poor fit (a failing of the installer) and it's a pig of a job to have to refit each one and hold it in place. I'm using rolls of seam-tape stapled onto the beams. I must upload photos of some of my DIY work one day!

Thanks 10-10-20. You've been a massive help. I really appreciate it. Would love to see the work you had to do to repair your own job.

lfcjfc

Viking House wrote:

You are creating a non-breathable roof there leaving the rafters as the only escape route for moisture leading to a build up of moisture in the wood. I would have preferred a more breathable safer solution. You can put a vapour control layer internally but it is extremly hard to get it airtight.

The U-value in Polyeurethene is not stable and is dependant on trapped gas which migrates leaving a worse U-value. Try holding a match beside a broken piece of new and old Kingspan and you will see the gas ignite in the fresh product and the older material has no effect on the flame.

Polyeurethene is only 22kgs/m3 and is too lightweight to prevent summer overheating in your attic. It also has the effect of loosing heat quickly similar to the way your caravan gets like an oven an hour after the sun comes out.

Lightweight insulations are for foundations and heavy insulations for the roof and walls.

Sorry for the news but its the truth!

Hi Viking House
Do you have any more information on the stability of polyurethane insulation. Would be interested to know the impact of time on thermal resistance - how much will the u-valuer change? Trying to decide on what type of insulation to use in a new build at the moment.

10-10-20

<SNIP>


I'd suggest creating a new thread for this topic. You're going to get more replies.