Tips for Rigid Full Fill Insulation (yes, I know!)

[BadgerBadger]

Right then... I've ignored all advice, and we've specified a full fill rigid insulation (well 15mm residual cavity) using Kingspan Kooltherm for our build.  I'm aware this is going to be tricky to get right, but we didn't really have the option of going much wider with the cavity, certainly not wide enough to get the same nominal U values with other options.  Of course the actual U value depends on how good the installation is - it's now crunch time and we're about to begin!

 

We have some good brickies who seem to have a good eye for detail, and our plan is to work around them doing the really time consuming bits and spending the extra time to improve their best efforts.  So any tips?

 

Specifically:

How best to cut the rigid boards, particularly around intricate details like our periscope vents?

Inevitably there'll be some gaps between boards in some places, can these be filled with an expanding foam?

[Redbeard]

For fiddly little cut-outs you can do a lot worse than a bread-knife. The special insulation (hand)saws you can buy are effectively just that. You can buy insulation blades for reciprocating saws but I challenge you to stop the blade waggling (i.e. your cut looks great on 'your' side of the board and is say 50mm out at the back!). I gather Festool do something wonderful but I am afraid i have no details. Yes you can fill with expanding foam, but the lambda value is not (AFAIK) the same, so keep it to a minimum. However if you try to fill really narrow joints (say less than 3mm wide) you will probably find yopur foam only goes a few mm deep. Do some test-pieces.

 

Good luck!

[BadgerBadger]

I now done a couple of small fiddly areas. It takes time but seems to be going reasonably well, so I'm optimistic we can get a good result!

 

I seem to be getting good results cutting with a fine tooth saw.  I've tried one of the glorified bread-knife tools, but as it cuts the insulation it tends to wedge into the cut, becomes very difficult and pushes off course.  As the saw removes material it's cut through quite easily, but does make a bit of mess!

 

Some small gaps are pretty inevitable but a can of low-expansion foam seems to be working well and filling them nicely, cut flush and then taped over.

[Roundtuit]

I cut ours with a bog standard hand saw; you'll soon get your eye in and be able to cut it to a snug fit with minimal foam required (a fraction oversized also fits if you apply a batten and a lump hammer😉).  The dust is a b@$tard; wear a mask keep hoovering up!