Vapour barrier and insulation for new workshop

First off, never have glasswool touching the internal face of a solid masonry wall. thats a big no, no. Glass wool is a recipe for big problems later on when used for an external wall.

The easiest way and a very efficient way is to use Triso super 10. Very effective, vapour barrier / insulation all in one. Simple to instal. I think it is equivalent to approx 200mm glasswool. Used a lot now on both new builds and renovations.

There wasa comment earlier about woodburners releasing moisture. Realistically any combustion vapour will go out the flue and actually draw air into the fire and out of the shed so ventilating and removing moisture. The only problem with them is the darned dust and ash from logs and cleaning.

<can of worms alert>
Thinwall multifoil insulation such as Tri Iso 10 (and Tri Iso 9 before it) are effectively useless in the real world of planet earth where conductive, convective and radiative losses occur. In the vacuum of space with huge temperature differentials they are quite effective and have a role to play. UK Building Approvals were iirc withdrawn at one or more points in the past.

The Advertising Standards Authority have also upheld more than one complaint iirc. The testing regime also made an appearance on TV, maybe Watchdog? five or more years ago. The word bargepole springs to mind.

**LINK**

A sheet of foil faced PIR, even 12mm will probably perform significantly better.

In my workshop it's 50mm underfloor, 75mm walls and 100mm in the roof, all in foil faced PIR. 1000gsm vapour barrier on the internal side, tyvek breathable membrane on the outside. The external heating / cooling requirement is close to zero regardless of the external conditions.

As you say, its been around and in use for ages. I used a quilt insulation on the loft conversion in our Cambridge house about a decade ago and it seemed to be pretty effective to me. Without having done any hot box testing myself (regardless how realistic they are), I have no objective means of evaluating it but the experience in cold winter and hot summer was quite convincing compared to previously. Having said that, I fitted it all myself, so made certain there were no gaps or cold bridges, which is possibly where some installations come to grief, knowing how builders like to cut corners and possibly don't understand the subtleties of installation.

Incidentally, the workshop / dining room extension we are currently finishing off has 1" of polystyrene and 3" of rockwool in the cavities (polystyrene next to the outer skin) and the roof has 4" of Eurothane GP (polyurethane foam) between the 6" joists (under a breathable waterproof felt) and an additional 1" of the same foam over the underside of the joists. The plasterboard will sit on the inside of that. We could have used a quilt instead of the foam but it's more expensive and is best saved for when you want to save a few inches of space eg in a loft conversion where head height etc is valuable. And yes, it's been signed off by the local planning officer here in Lancs.

Murray

Well Muzzer, you have it in a nutshell re the quilt insulation. If it does not perform as it is specified to then it can usually be traced back to the installation. although it would have been more apt if you had said SOME builders and not lumped us all in the same category....

Worked on a new build some months ago. It was a nursery for Aberdeen UNI and the style was "PASSIVHAUS "

All penetrations through the insulation in the cavity had to be sealed even a single cable. Inside kit was 200mm thick as opposed to the usual 140mm None of the normal double or triple glazed sealed units for windows, these were special types, same with the external doors and frames. Even the cills and door soles were a special rigid plastic, not the normal pre cast units. Never worked on a building like it before. At the completion it was the subject to a barrage of tests and had to pass them all.

It is reckoned to be so efficient that the whole nursery can be heated / cooled with only 7 % of what a normal build would need using traditional practices and materials. The whole build was valued at 1.3 mill which is about double of what a "normal build of the same size would be. Although look at the savings on energy costs.