Insulating doors through knee walls

blast06

Hi,
Timber work almost complete on the roof of a new build dormer. I have 2 rooms upstairs but also have a lot of available attic space (~75% of overall floor space in house is downstairs). My question is how to create fully insulated doors through the knee walls (that are as air tight as possible) into the attic space. I will probably have 1 in each room.

I plan on have 70-80 mm insulation backing up against 50mm insulated slabs on the 5 feet knee walls, 100mm insuation along the rafters, house will be airtight etc etc ..... but don't want to almost undo all this investment by having sloppy, poorly insulated, drafty doors through the knee walls.
Any ideas of any 'specialist' products. Doors need be no bigger than say 100cm high

Cheers

Poor Uncle Tom

Why not look at re-cycling the door and magnetic sealing strip from an under worktop fridge?

MicktheMan

blast06 wrote: »

but also have a lot of available attic space (~75% of overall floor space in house is downstairs).

Available for what exactly? This "space" is outside the thermal envelope, the same as a good wooden garden shed!

Going to the effort of making a dormer airtight and then putting access holes through the airtight barrier into the attic is, imo, madness.

If you really want to install airtight access then you need to think about a well sealing window (sealed to the knee walls) as a door access for this area.

Btw, what is your airtightness target?

blast06

Thanks for the replies.

I don't have access to the BER advisory reports for air-tightness off-hand. I have a figure of 0.150 in my head but not sure if this makes sense ?

Anyway, what i am trying to determine is if there is a practical way of creating this entrance to the attic space without (overly) compromising the thermal envelope .... in the same way as opening and closing the front, back or side doors. Wondering if anyone has any experience of doing this ?
The benefits of me doing this are that i would have easy access to approx 50m2 of storage space ..... by putting a 2nd layer of joists (7" x 2") perpendicular to the the first (9" x 2") and putting sheets of marine ply over these with slabs on the undersides of the rafters. I need the 16" of joists to meet total wool thickness requirement.

I'll look into the magnetic strip idea. I guess in theory it should do the trick and have say 70mm polyiso or some such equivalent attached to the attic space side of the door.

Cheers.

MicktheMan

blast06 wrote: »

1. I don't have access to the BER advisory reports for air-tightness off-hand. I have a figure of 0.150 in my head but not sure if this makes sense ?

2. Anyway, what i am trying to determine is if there is a practical way of creating this entrance to the attic space without (overly) compromising the thermal envelope .... in the same way as opening and closing the front, back or side doors. Wondering if anyone has any experience of doing this ?
The benefits of me doing this are that i would have easy access to approx 50m2 of storage space ..... by putting a 2nd layer of joists (7" x 2") perpendicular to the the first (9" x 2") and putting sheets of marine ply over these with slabs on the undersides of the rafters. I need the 16" of joists to meet total wool thickness requirement.

1. 0.15 equates to 3 m3/hr/m2 airtightness. Is this specified in the contract with your contractor and how does he propose to achieve it?
I assume you have planned for a good ventilation system at this airtightness level. Something like DCV or MVHR.

2. It's good you're thinking like this. All too often there are verp poorly sealing access doors fitted to the dormer attic allowing a hugh amount of warm air out the roof and causing severe draughts down stairs.
A well fitted door with latches and sealed using a variation of this will work well as the door won't be in daily use if only used to access storage.

blast06

Thanks.
Its a direct build and i haven't agreed with any supplier & fitter yet re the airtightness. I have a quote (with details) from one and it is there he mentions the .15 so i guess that is pretty good ? I haven't gone through it in detail re how he will achieve this but the price includes 2 tests as well. This price was based off plans
I have 2 more guys coming to the site between now and mid next week to review and give a price so will hopefully have finalised things by next weekend.

Any tips on other things to look out for ?! ..... or if you're in the business yourself then PM me !
One concern i have is that the block work for 4 or 5 of the windows is a bit sloppy where the gap at the top of the windows (mostly 1700 height) is about 2-3 cm less than at the bottom. Does this just mean wider tape like say here: http://www.theinsulationstore.ie/product-details.php?ID=159

Cheers

MOTM

Bought a house last year - one of the bedrooms had a knee wall door with no latch, no seal and no insulation. The room of course was freezing as a result. My solution (not ideal but the room is now as warm as any other): I put a latch, draft stripping and 50mm insulation. Works really well.

MicktheMan

blast06 wrote: »

or if you're in the business yourself then PM me !

pm sent