Workshop Insulation Problem

Hi Dave,

Have you insulated the walls and sealed the floor ? they will be a source of damp ingress.

Like you I 'created' my 'man cave' otherwise known as my workshop in a brick built garage, (didn't have any choice really) and so far (touch wood) I have not had any damp issues, my tools and metals seem to keep rust free, so I thought I'd share how I insulated it.

I lined the walles with a thermal wrap **LINK**

I literally hung it like wall paper from floor to roof, dab fixed with a cheap verion of no nails adhesive, then I applied a layer of celox (like you have used) I used the 15mm version, then a 6 mm ply covering to finish off.

For the roof, I used good old fasioned loft insulation, again with a ply cover to finish, then I have painted the floor with a sealing floor paint.

For the winter months I have a 2kW panel heater which comes on for 5 minutes every hour (on a time clock) to keep the chill off and humidity low, and so far it has worked a treat.

The only difference to you is the loft type insulation which may allow more air flow than sheets of Celotex in the roof space.

I sorted a similar problem for a client last year to the tune of £50K.

As their's was the gym and changing rooms adjacent to a swimming pool there was no shortage of warm moist air which found it's way up through the plasterboard then both rigid and fibreglass insulation where it promptly condensed back to water on the underside of the roof boarding which was worse as the outside temperature dropped. Water was literally running down the underside of thesloping boards and then down the walls and you could wring out the fibreglass like a sponge. There is a reason this type of "cold deck" construction is seldom used these days.

Both Building control and specialist consultants agreed that there is no way to totally seal the room as moisture will find small gaps around cables, downlighters, abutments etc so as well as providing 3 levels of vapour barrier ( Foil backed plasterboard, polythene dpc and taping insulation joints) the recommendation was to ventilate the void between the top of the insulation and the roof decks.

This took the form of continuous eaves vents at the bottom of the sloping parts and continuous ridge vents at the apex. The flat roof areas has continuous vents at either end of the main joist runs for through flow. Also a few soffit vents for dead spots.

Edited By JasonB on 07/05/2020 20:53:03

THis is why you have to have a vapour barrier that is 100% not just 99% though it is difficult. Since you are using rigid insulation panels you need to arrange a 1 in gap above them with spacers and provide a way to vent that space out to the air not to the inside. If the roof boards are straight onto the rafters making individual compartments then each one has to be vented.
if this or a forced air circulation is too difficult then I suggest making the insulation deliberately vented to the inside but running a dehumidifier a lot at a low humidity setting so the damp is encouraged to re-evaporate back inside and get removed.

I can't comment on the structural side of things, but like Bazyle, I run a dehumidifier in my brick built double garage with an insulated flat(ish) roof. I have it set to 40% humidity and I'm collecting a couple of litres of water every two or three days to once a week depending on outside humidity.

I haven't seen any damp issues in the garage but I run the dehumidifier to help keep my motorcycles and metalworking equipment rust free rather than to deal with structural issues.

I’m possibly not like Bayzle (he doesn’t state that he actually runs a dehumidifier! (chinese whispers?)) as I really do run a dehumidifier - a desiccant type - for a short period each day, most days.

It not only effectively removes moisture from the air at lower temperatures (some dehumidifiers state performance at monsoon-like conditions and don’t really work efficiently at UK temperatures!) but also provides an amount of heating, to keep the temperature up, in the cooler months. My small workshop is fairly well sealed from the outside and heavily insulated, it being covered on sides and ceiling with at least 100mm of insulation.

Thanks for all the replies,

I don't have a problem with damp/rusting tools etc in the actual garage /workshop. The wall on one side is the wall of the house, and the other side is the neighbours garage which is attached to their property. The door is an insulated roller door. The access from the house is a fairly well sealed door. I can move the lighting cables to underneath the insulation in conduit to remove holes through the insulation. If I then seal /tape all joints to form a complete vapour barrier this would leave the roof space completely un ventilated, is that a good idea?

iNf

Dave

I think there is still a problem if the roof interface is completely sealed as a vapour barrier is never 100% and so the void 'breathes' hot moist air in which condenses. In summer the hot roof will work it the other way round but in the UK climate the two periods don't compensate. The choice of barrier position is more complex in a continental climate where it may favour the barrier on the outside.

I don't run A dehumidifier as in only one. Last night I had 3 running until the bedroom one filled but I actually have 6 altogether. The sensor has just turned the living room one next to me on again. I am in a very damp part of a damp county. All are compressor type as I can't afford much electrical heating and mostly run them overnight on the cheap rate where I also get the benefit of the extra heat of de-evaporation. Contrary to popular wisdom they do work down to freezing. The reputation for not working when cold comes from America where cold means well sub zero not the mild UK. Owing to the 2ft thick granite walls the house temperature never goes below zero but the store shed with only 2 in insulation does but is still collecting water then as the door is not sealed.