Closing 300mm cavity

fealeranger

Hi folks,
Anybody have any ideas about closing a 300mm cavity around doors and windows and finished walls. I have seen a few products which I obviously can't name but any info wolud be a great help.

fclauson

there are a number of techniques in common use (as common as there are 250mm/300mm cavities)

not naming any specific products there is

• the ply wood box method
• the insulaiton board method (using the rigid board to block of the cavity) then plaster board
• the fiber board method (allthough check with manufacture about moisture/damproofing etc)
• a couple of different propriatory closures which are fabrications of narrower cavity closures

What you have to ask youself is what is its purpose
a) to stop bead flooding out when pumped
b) to stop the migration of moisture across the cavity
c) as a fire stop
d) to sit on as a window sill

Windows in these wide cavities are typically strapped back to the inner leaf using multiple straps so @ 300m you will need to ensure you/your eningeer are happy with how this is achieved in a robust methodology

One word of warning - my engineer commented and will not sign off until resolved (and you will need to check with yours for their interpritation of the regulations) that the cavity closure method at the top of the wall must be class A fire rater to stop fire spread wall to roof/roof to wall

:eek: oh I fogot the old fashioned L block could also be used :eek:

fealeranger

fclauson,
There is a product there made from PVC that I was looking at, I PM,d the details to you. It is PVC, Fireproof, prevents cold bridge and keeps in the pumped bead so it satisfies all the points you mentioned above. My doubt with it is if I ever have to change/get new windows would this get damaged in the process. The top cavity will have a block accross it so that will take care of fire spreading.

fclauson

For windows:
We looked at the product you PMed and even spoke to the engineer and designer. The challenge came around the window still - here in Ireland we use Granite or similar and hence the window is not a true rectangle. So the cavity closure at the bottom would have to be fudged to make it work.

Up the side of the Jambs and at the head we have a stepped lintel i.e the inner size is a bit smaller than the outer to allow for a robust detail at the inside of the outside leaf. The product you suggest is not ideal for this as it assumes same inside and outside.

Lastly its expensive coming in at about 3 times the price per M than most other methods - so all in all - good idea but failed on some key criteria

BarneyMc

fealeranger wrote: »

fclauson,
There is a product there made from PVC that I was looking at, I PM,d the details to you. It is PVC, Fireproof, prevents cold bridge and keeps in the pumped bead so it satisfies all the points you mentioned above. My doubt with it is if I ever have to change/get new windows would this get damaged in the process. The top cavity will have a block accross it so that will take care of fire spreading.

Can you PM the details to me please fealeranger?
Thanks, Barney

fealeranger

Pm sent Barneymc.
Any people who have built these 300mm cavity wall can you Pm me how you closed off the window and door openings as I'm out of ideas as what to do?
Are L Blocks a bad idea as Structural integrity keeps flashing accross my mind when I think of this wide cavity. A partial return on the inside and outside leaving a gap of 100mm at doors and windows would strengthen up the whole show but that is just me thinking. I'm not an engineer but this seems to stand out for me. It does not form a cold bridge and is solid.

fclauson

fealeranger wrote: »

Pm sent Barneymc.
Any people who have built these 300mm cavity wall can you Pm me how you closed off the window and door openings as I'm out of ideas as what to do?

PMed

Are L Blocks a bad idea as Structural integrity keeps flashing accross my mind when I think of this wide cavity. A partial return on the inside and outside leaving a gap of 100mm at doors and windows would strengthen up the whole show but that is just me thinking. I'm not an engineer but this seems to stand out for me. It does not form a cold bridge and is solid.

It does form a cold bridged for the following reason the U value where you have the L will be much higher than elswhere - hence will be colder (more heat cold can "leak in" at this point

BarneyMc

fclauson wrote: »

For windows:
Up the side of the Jambs and at the head we have a stepped lintel i.e the inner size is a bit smaller than the outer to allow for a robust detail at the inside of the outside leaf.

What's the reason for this?

BryanF

was this not covered a few weeks ago.. http://www.boards.ie/vbulletin/showthread.php?t=2056565140

fealeranger

That little steel fixing angle is a good idea. It could work very well for me.