Insulation Questions

Lemlin

Hi folks,

I've a 100mm cavity space to work with in my walls so I'm planning to go with a 100mm bead fill which should give a u-value of about 0.27 in the walls.

However, I'm wondering about my attic. I had planned to go with about 100mm rockwool but I've heard about foaming now for the attic. However, one provider has already pointed out that its expensive. My attic is about 17 foot by 40 foot and (as per another thread) I plan to install a membrane but how much would I be looking at to foam insulate? Is it worth the extra cost? I had mentioned using blown rockprime to one installer but they reckon they prefer to install foam in new builds.

I also plan to scratch coat the walls on the inner leaf of the house.

In terms of insulation, what should I be aiming for?
Also, is there any method I could use to get a better u-value than 0.27 for my 100mm wall cavity space?

Budget is also an issue of course. I want to get the best value I can for my money.

sinnerboy

The walls

To get to 0.27 W/m2 K U Value you will need
1. beads with a certified lambda value of 0.33 W /mK ( If you don't specify you will get beads at 0.04 ) and
2. quinn lite or similar blocks to the inner leaf

Otherwise you will only get a U Value of 0.34 W/m2 K

The roof

You need to get to U Value of 0.16 W/m2 K - so min 300mm Rockwool .

sinnerboy

.... using quinn lites to both wall leaves will get you to 0.26

Lemlin

sinnerboy wrote: »

The walls

To get to 0.27 W/m2 K U Value you will need
1. beads with a certified lambda value of 0.33 W /mK ( If you don't specify you will get beads at 0.04 ) and
2. quinn lite or similar blocks to the inner leaf

Otherwise you will only get a U Value of 0.34 W/m2 K

The roof

You need to get to U Value of 0.16 W/m2 K - so min 300mm Rockwool .

What will 300mm of Rockwool cost me in comparison to spray foam insulation though? I've also been looking at the Rockprime from Rockwool which is a blown loft granulate insulation but one provider said they preferred to install the spray foam to new homes. I'm wondering is this because its cheaper though.

I've already used standard blocks and not quinn lite so is 0.34 the best u-value I can hope for from my walls or can I do anything inside to improve this?

sinnerboy

You need to dry line using min 25mm PIR Kinsgpan or Xtratherm + Plaster ("Cosi-board ")

Lemlin

sinnerboy wrote: »

You need to dry line using min 25mm PIR Kinsgpan or Xtratherm + Plaster ("Cosi-board ")

Does drylining go onto the inside walls? I planned to use insulated slabs. Will this help?
I plan to scratch coat the inside walls for airtightness.

sinnerboy

Yes.
Thats what I am talking about .
Yes.
Good .

Lemlin

Someone had mentioned <snip) to me for insulated slabs?

Mod Edit
Any threads naming specific companies/traders will be deleted. Exceptions to this will be at the moderators' discretion.

Smcgie

Lemlin wrote: »

Someone had mentioned <snip> to me for insulated slabs?

I don't recommend <snip> we order stuff before and quality and after services is nowhere near their competitors.

S.

Any threads naming specific companies/traders will be deleted. Exceptions to this will be at the moderators' discretion.

sinnerboy

Larger businesses may be named as they dont really need any "free plugs" but the forum may not be used for highlighting any other businesses unless the moderators decide that it would be beneficial to the wider community. This is done to ensure that the community get good advice and free from those who would seek to gain by promoting a particular product or by having a vested interest in the business or it's products.

In no circumstances should any business, large or small, be praised from the heavens or condemned into hell in any thread on the construction and planning forum.

Regarding the latter it should be noted that the forum is not to be used for people to condemn any business or product as that is a consumer issue and not something that should be discussed here.

Lemlin

sinnerboy wrote: »

You need to dry line using min 25mm PIR Kinsgpan or Xtratherm + Plaster ("Cosi-board ")

I'm going with 50mm insulated slab. I presume I'm fairly well insulated then with 100mm cavity bead, 50mm insulated slab and then a scratch coat on walls for airtightness and membrane at draught areas.