Sweating and mouldy New cold flat roof

So wouldnt you say that this building has been built to a good standard and to spec . Yet it still has these issues doesnt that tell us that somewhere along the lines it doesnt work

In my experience anyone who calls themselves a builder isnt actually trained or qualified. You need to be at degree level to properly understand the all the areas of construction. I employ the correct trade for each stage not a builder who thinks he knows it all.

i have just recently done a cold roof, pitched, vaulted ceiling. the architect specified 170 x45 c16 with 150 Kspan pushed up tight to the underside of sarking with a 3mm gap between boards now 10mm after the sun bashed it for a while, got a breathable membrane and 12mm counter baton and 25mm baton then concrete tile. on underside of rafter he did ask for kingspan kooltherm 118 however client thought this was too expensive and opted for 25mm recticel then a vapour barrier then 12 .5 plasterboard. Have i got something to be worried about in the future???

Counter batten underneath 🤷‍♂️

hi , thanks for video ! planning my new roof , same cold roof , joists hanging on the wall with hangers , got the walls from sides .. need ventilation! how is better to do .. go battens along the joists then across the joists ? need 2 layers of battens or one ?! thank you

your videos although a few years old, are proving really useful to me. However, can I ask, if I fit a vapour barrier over insulation like can be seen in this video, would the screws of the plasterboard fitted afterwards compromise the VP ?

It is, frankly, shocking how poorly understood the subject of proper ventilation is in the building industry. My theory (or part thereof, at least) is that in the UK, so few builders appear have had a formal education in 'building'. Mind you, if architects/politicians don't understand it/know about it, how can we expect builders to? The other part is, basically, that people being people, if they can cut a corner, they will! This issue goes very much hand-in-hand with the lack of understanding of effective installation of rigid insulation boards (RIB). How interesting that this DIYer managed to 'get' the need for foaming in RIB rather than just relying on an industry-standard (in my experience) 'interference fit' - which almost always leaks air like a sieve - and the majority of 'professional builders' simply haven't the foggiest idea for the need (now part of the building regs, I gather?) - even if he did make the fairly colossal error of failing to make adequate (any!) provision for cross-ventilation around the sky-light... Anyway, keep up the good work!

Amazing vid..thx Steve

Should he use treated lumber inside the weather barrier, really? You obviously could if you wanted too, but it is not required or at all common.

Informative

Hi steve, i have a question, i have a small extension with a warm roof and a overhang on the front there is a secret gutter, the inside is not plasterboard yet, and we had a lot of rain when roof was done, my problem is where the overhang is the osb below the secret gutter is sweating. I was told to pack this with insulation to avoid drafts, at the moment there is no insulation in there and with the cold frost in the morning i am guessing that is causing the sweating. Do i fill this with rockwool or pir, i plan on having downlights in the sofit.

Hi Steve great videos and very useful. I'm not in London but I have an old house that is poorly insulated. I know now (your videos) that I need to seal the insulation in place. And then cover with more insulation but I'm concerned that if I close all the air gaps that the moisture won't get out and then start to cause problems. Just to add to the amount of moisture there is in the building we live in a flood plain. The Victorians dealt with this by having large voids along the roof but this is now costing us.

Brian

Which vapour barrier do you recommend,? And would this be simply stapled to the under side if the joists?

Absolute bolox

This is would be a really short video, only needing 2 sentences.
Use spray foam closed cell insulation, not open cell insulation. No ventilation needed Closed cell insulation is also a vapor barrier problem solved. . Not to mention in the UK the average temperature in winter at night rarely freezes. Where I come from summer times in the nineties cold winter nights close to zero temperature. I’m from the state’s retired contractor

Can I do cross battens for side(s) ventilation aswell as front ventilation without venting the rear?

Hi I’m starting a model railway in the garage. Please can you advise on insulation and condensation? Thanks

How are people getting this type of thing past building control? And who is designing it all ? The architect engineering drawings should flag all these schoolboy errors up. Or is this guy and a lot of people on this comments section making it up as they go along? Thats all fine but just wait until you try and sell the house.

Could you advise how to remove condensation from bottom of onduline roofing fitted on my shed. No insulation on walls so far. Just timber walls with shiplap cladding and timber rafters with onduline on top of them. Roof angle about 10 degree.

As a sparky I found this really insightful. I’ve watched a couple of your videos now.
I often come up against clients and building inspectors regarding the cut outs for my downlighting and the ways around it to still keep a good barrier.
I’ve always wondered what the main differences between cold and warm roofs and the benefits.
Thanks for the videos mate

What is your email address please I need your help

Hello Steve I need a small extension roof done in London can you come down and price up please?

Great video! With a vapor barrier applied on the underside of the joists, won't it just be punched full of holes with the drywall screws?

Good job Steve. I wish more builders paid attention, like the subject of this video. Carrying on regardless, I think, is more common than it needs to be. It's OK to make a mistake, even the good builders do it... the difference is the good ones put it right!

Great video and great explanations, currently doing similar and watching that my builder is venting properly. My only concern with mine is we are having spotlights and see plenty done like this is there are correct way to fit spotlights without them causing problems

Takové zásadní chyby v projektech u nás neděláme....

Another great video Steve! I'm building a flat roof extension to an old property in which I have very limited headroom, limited to where the new roof tucks under/into the existing roof, therefore the flat roof build up has to be minimal, while maintaining best possible u-value. At 3m span I'm using 145 x 47 timbers, 400 centers. My planned build up is: 12mm plasterboard- 145mm timbers containing 100mm mineral wool- multifoil sf19 insulation over rafters pinned down by 38mm battens. 18mm osb3- epdm membrane. The sf19 acts as a vapour barrier, no ventilation. This gives a total build up of 220mm, leaving just 2090-2040mm headroom in the bedroom below. Does this sound feasible to you, or do you have any suggestions on how it can be improved?
Thanks, Colin...

So you need a gap behind the kings pans and a gap at the front of it to keep good airflow

A sound and fair analysis, you can solve the cross ventilation problem by the way by instead of using roof joists constructing shallow pitched trusses out of 3" or 4" x 2", they are very strong but whatch out that you don't get a moron building inspector who insists upon solid 6" or deeper x 2" joists because he learned his job from books and specification sheets and doesn't have an ounce of common sense.

Learn to build properly before you start. No sympathy for these fools.

Why wouldn't you just put the insulation where it belongs, on the exterior, ABOVE the OSB , and forever eliminate all these issues, let alone try to execute the impossible prickly details of sealing for vapor and venting on the warm side ?
This assembly is built to fail, no matter how well you think you've sealed it...

This is the perfect mancave video. A video on how to build a mancave. 😀 for cavemen by cavemen. Nice video!

I bet his neighbour loves him lol

Does the closed cell insulation with foil backing, along with foaming air gap details not suffice as a vapour barrier?
Foil has a superior vapour Impermeability than poly even.

Very knowledgeable person
Love take you advise for my flat roof under construction. Already leaking .

Love your videos, really informative. Fantastic 👍🏼
Would love to see a video on how to correctly install spotlights into a cold roof, I just can't find a good source of information on this!
Keep up the brilliant videos 👏🏼

Hi Steve, that's a really informative video. Thanks! Could I just ask...do I need a vapour barrier on my internal walls and ceiling in my garden room that I am building. There will be no heating in it but is going to be insulated with 50mm Rockwool in the walls and 100mm Rockwool in the ceiling leaving a 50mm gap in the ceiling for airflow to the soffit vents I have in the front and back. (It's a flat cold roof by the way.) The reason I ask is that I have read that a vapour barrier will not allow the colder temperatures at night to get rid of any moisture. It apparently traps it essentially in an unheated build. I'm not sure if this is accurate and wondering if you could shed any light on it for me? Many Thanks

Hi mate i have a single brick garage in highlands. I will be installing a insulted roof.will this be enough to keep it warm to do a work out in if I use a heater to heat it before my workout it will just be the roof that is insulted

Good Video great advice

Really excellent review of the job, a lot of really useful information. Good job. Thanks give me a lot to think about

Hi Steve. I have a flat roof garden room with joist running front to back. The left hand side of the roof has been cantilevered off the front to back joists. How would i overcome the cross ventilation for the cantilevered section?

Agrees with everything but the need for treated lumber.

Rule 1 only do warm deck

The End

As an electrician. Can down light not be fitted into a flat roof due to the insulation removal??

Hi Steve! Great work on the video!
Out of interest, do you know what lintel was used over those bifold doors / width of opening?

Great video !

-64 dislikes....Must be from builders who have been rumbled by this video.

Hi Steve. I'm planning to convert my small shed into a sauna. How could I stop the condensation to damage my roof? What would be the best insulation for the sauna roof?