Attic Insulation

gears

I was at a friends new build lately and I was wondering if anyone has come across this approach to attic insulation.
Instead of using 10"+ of regular attic insulation he plans to use a 40-50mm insulated plasterboard (kingspan I think) with 6" of additional attic insulation, this is so he can still use the attic for storage. Also he is planning to use something called "Thermohemp" for the attic insulation, anyone heard of this product before ?
Using the insulated plasterboard is new to me, but is probably commonplace and I thought it was a good way to get around the storage v's plenty of insulation in the attic.

Mellor

I take it that your friend is insulating along the flat of the roof (first floor ceiling). And he is doing it this way so that the joists will be filled, and extra laid under the joists, as opposed to the more common crossing laying of another layer above the joits, which gets into all sorts of problems with walking about the attic.

If you are insulating this way, a breathable felt isn't required as eaves ventilation is possible. the insulated plasterboard comes in a number of forms, mostly rigid slab type, although moy do a glass wool back one but its not really suitable dor this area.
Extruded polystyrene (instead of expanded) is good, pheonlic based is probably better. Kingspan do both.

as for thermohemp, i imagine this is for the attic joists. Its an organic insulation, they have a good web-site and are a decent product.
its worth having a look through the data shetts for get values for proformance.
But take everything with a pinch of salt, as often these products twist figures to suit themselves. But thermohemp is still as good as basic glass insulation
http://www.ecologicalbuildingsystems.com/products/thermohemp/detail.shtml

ardara1

foyc wrote:

Using Kingspan without a breathable liner, will end up in disaster, whole roof back off.

The new evaluations of thermal insulation set by the EU regs due in on the 1st of Jan 2007,

There has been no change in the way that thermal insulation is evaluated - there are changes to the way in which energy perofrmance of the whole house is evaluated. Thermal performance of individual products or elements, walls, floor or roof remains unchanged.

There is no necessity to use a breather, can you explain why the lack of one will end up a disaster?

There's quite a bit of debate on the use of breathers.

dixiefly

One of the reasons for using an insulated plasterboard is to eliminate the heat "sink" that occurs when you only insulate betwen the joists. Most of the major insulating people like Kingspan, Hytherm & Quinn do an insulated plasterboard and Gypsum do one as well.

ardara1

foyc wrote:

A few local builders had to go re-felting, after they had used standard none breathable felts in some of their attic spaces that had then been insulated with Kingspan.

A moisture trap had been created and there was extensive water and moisture coming through the kingspan boards shortly after they built the houses.

The massive lesson they told me they had learned, is always use a breathable felt liner under roof slates in attic conversions, or suffer badly.

They had to reroof using the breather membrane because they forgot to maintain the necessary 50mm ventilated void underneath the ordinary felt and the insulation.

Excessive moisture is present in all new builds and steps such as leaving windows open should be taken to allow the wet trades to dry out before sealing the place up - putting a breather membrane would not have changed this situation.

The moisture was not caused by the kingspan board - I wonder what thickness they put in the rafters?

Mellor

Besides, the example used relates to a roof with the insulation along the pitch of the roof. The original post relates to joist level insulation.
A breathable felt is an alternative to a venilation space, but it is not the only way to do it.

Viking House

Mellor wrote:

But thermohemp is still as good as basic glass insulation

Thermohemp is better than glasswool for a number of reasons, being hydroscopic, it can transport water vapour through the material and dry itself and the wood beside it in the process. Glasswool on the other hand stays wet when it gets wet increasing the moisture level of the wood around it. Even though they have similar U-values Glasswool lost heat a lot faster than thermohemp in German trials.

Mellor

Viking House wrote:

Thermohemp is better than glasswool for a number of reasons, being hydroscopic, it can transport water vapour through the material and dry itself and the wood beside it in the process. Glasswool on the other hand stays wet when it gets wet increasing the moisture level of the wood around it. Even though they have similar U-values Glasswool lost heat a lot faster than thermohemp in German trials.

I know thats true of sheeps wool insulation, but never seen it mentioned in the thermohemp leaflets. Is it on website? I had a look at it at one of the shows, but left soon as the spokesperson was throwing a few white lies in with his claims. Rather than let the product speak for itself.

Viking House

Hi Mellor

I have an interesting document in a pdf file stored on my computer on this topic. I tried to post it on this forum yesterday but failed. Maybe if I emailed it to you could get it up on this forum or maybe somebody could tell me how to do it.
The document explains how different insulation materials worked differently at holding on to heat in a house.

construct06

just to clarify

---

is it the case that:

1. if u are using normal roofers felt, a 50mm air gap must be maintained between the insulation (kingspan or wool) and the rafter

2. if u are using breathable felt, no 50mm air gap needed between the insulation (kingspan or wool) and the rafter

if this is not the case what are the advantages of using a breathable felt?

Mellor

construct06 wrote:

just to clarify

---

is it the case that:

1. if u are using normal roofers felt, a 50mm air gap must be maintained between the insulation (kingspan or wool) and the rafter

2. if u are using breathable felt, no 50mm air gap needed between the insulation (kingspan or wool) and the rafter

if this is not the case what are the advantages of using a breathable felt?

It depends on the insulation, with quilt types insulations, i'd go for the gap to be safe. Boards type can be used with either type.


Viking House, how big is the file as the limit for pgfs is about 244kb. It may need to be hosted somewhere for viewing, somebody here might be able to help.

Viking House

368 kb is the size of the file

cuculainn

Viking House wrote: »

368 kb is the size of the file

Hi Viking house, just came across this post. would you be able to put up this PDF or email it to me?

Thanks
Cuculainn

paddy147

cuculainn wrote: »

Hi Viking house, just came across this post. would you be able to put up this PDF or email it to me?

Thanks
Cuculainn

4 years too late mate.

cuculainn

paddy147 wrote: »

4 years too late mate.

Thanks for the helpful reply in stating the obvious....BUT its never to late, as I got a PM with the info.