Great video - I'm a Building Surveyor and dealing with a disrepair claim like this in London at the moment (acting for the Landlord). Interestingly, the walls in this claim were pumped with insulation which caused them to perform better thermally and the cold spots moved from the walls to the ceilings (due to poor insulated ceilings). I'd say first step is to minimise the condensation below and use an extractor fan in the bathroom which has a humidistat built-in. The location of the fan is key. Make sure that it's far away from the window as possible so that when you have a shower and open the window it draws air from one side of the room to the other. As it has an as-built humidistat fan built in, it will kick in when it senses high humidity and remove any remaining moist air even when the light is turned off. No drying clothes in the house either. As for the insulation arrangement, its easier to leave the ceiling in place rather than remove or overboard it (especially if it is covered with an asbestos containing Artex textured coating). I agree 100% of your assessment to seal the sealing as best as possible and then insulate over it and pack it tightly. Install an insulated loft hatch as this is always an easy detail for air in the room below to escape though. Ventilation is then the key in the roof space to allow this to work so allow for those roof eaves vents and add tile or ridge vents if required.

Installing vapour barriers around joists & other obstacles etc always looks fine on a CAD drawing... until you climb up into a dirty old loft to actually attempt it that is! As Steve already said: seal holes, protect vents & whack a load of new fluffy stuff down. Job done.

Thank you so much for this video, great review. I was thinking of doing something along the same lines, it was so useful seeing you review the options they proposed as we have a similar loft area. I will now be fitting vent protectors and layering up with rockwool

Thank you so much for this. I am adding insulation to an older garage with a pitched roof I use as a part time workshop. I just want storage in the loft. There is plenty of ventilation in the loft. Walls will be either PIR or rockwool between new stud walls with ventilation between the insulation and the outer breeze block wall. Yes it will be leaky from a ventilation perspective but energy efficiency due to only part time warm use isn’t my biggest concern. I kept worrying about sealing the whole inside with a vapour barrier when I have full sliced double swung doors on one end! I know obviously things would be different were this a living space.

I think this video may have just answered all of my concerns of insulating. I live in a 200yr old quarriers cottage, extremely well built with no signs of mould or condensation anywhere. Having pulled down a few ceiling now I can see there’s never been a vapour barrier, which I’ve been sweating over, but now I’m thinking that ‘vapour open’ is probably the way to go. I am replacing all of the old insulation with Rockwool. Fingers crossed this is the right thing to do.

great video. Fantastic drawings from the customer, that must make your life a lot easier. Just to clarify, the solution you'd recommend is 300mm or so of rock wool or similar applied directly to the plasterboard (no foil or anything), plus plenty of ventilation above? My loft has exactly that (maybe 400mm actually), so good to hear. I'm in a timber framed house and it's very well insulated (too well, it should have ventilation in my opinion, but I'm loathe to spend the money!).

One advantage of putting fluffy insulation between joists but PIR on top is that once the PIR is covered with wood you can have a use able storage space as long as it's only occasional foot fall. Just adding more fluffy insulation means for it ro become storage somehow you need to support a hard floor. One other issue that never gets mentioned is electrical cabling once covered by insulation is likely to need to be derated with smaller circuit breakers installing, cables in open air can take much more current than those covered by insulation

Ok, so I’ve insulated my ceilings this way. 75mm PIR cut precisely in between the joists without Vapor barrier, is been there for over a year and I can’t see any moisture around ceiling joist. Massive difference I’ve noticed winter nice and worm summer cool. One thing would stres enough is do not leave any cold spots as moisture would eventually make way down into plasterboard 15mm sound proof. Hope that helps

There is a trade off between vapor control & insulation performance. In an ideal world (such as a new build) insulation should be enclosed on both sides with an airtight layer, because this eliminates air infiltration for best thermal performance. However, as we see here in a retrofit situation, it's difficult to achieve integrity without stripping coverings such as tiles and ceilings to provide full access. It does seems to me like the viewer understands how this works, and if it's done VERY carefully it might work. However I also think your advice to go open cell is the best reliable solution. If it were me, I'd add a taped AVCL under the existing ceiling and over- board it. It's always easier to properly seal a flat surface than one with lots of timbers etc.

Love your videos Steve, could I put a request in, can you do a video showing the best practice way to join a sloping cold roof, to the warm roof section of a flat dorm roof

regarding air gap, regardless of keeping simple or not, the concept of radiant heat is that it radiates, it is not conducted by a solid material. The moment you don't have a void, there is no radiant heat and you are just conducting from one solid to another. So, from a physics perspective, the foil is useless if you have no gap, it will not work as a radiant heat barrier.

i have put a think layer of PIR (kingspan) under the joists and on top of the plasterboard, taped and foamed at its joints. So condensation wont creep up to the top of the joists. Surely this is better?

You recommend leaving the blanket insulation (rockwool) open & having a well vented loft,. But in doing so, could the moisture that gets through the ceiling reach it's dew point & condense somewhere inside the insulation (and not exit out the top) & so cause the insulation to be less effective & even compress & become even less effective? And if it stays in the insulation & not exit then mould could form?

Great video and pragmatic advice Thank you 👍

Roger Bisby staring in "The Ugly Truth about getting hits on KZfaq", I never get tired of getting tired about how many views he manages to get! I dread to think how many people he has lead up the garden path.

This is such a useful video and interesting to see a critique of those ideas in terms of making it simpler. So thank you. I am looking at installing a PIV unit but fear the unit drawing air that might hold airborne fiberglass particles/rockwool dust into the house. Is this something you've heard of or an unreasonable fear? Also wondering if a loft without felt - and just sarking boards, even needs additional vents before building up new insulation?

Steve, you're a star. Great document your viewer sent in, I've been going through the exact same (puzzled) process myself and I mentioned this graphic on here some time ago. That site promotes wool and 'natural' insulation btw. I commented on the eco-home site and the conclusion was: Eave Vents, then Tyvek Air Guard over joists/plasterboard + 200 min. Rockwool + 50mm air gap [NO air tightness layer] + OSB boarding over top. Rockwool was suggested as it's non-hygroscopic, so it doesn't hold moisture like fibreglass does, where some people blame it for rotting the timbers. Q. Are you suggesting not bothering with the Tyvek, and just sealing any 'open' penetrations? Laying and sealing the Tyvek does look like a real PITA so would it be worth it in the long run?

What about using no added 'vapour' layer, and heap insulation up in the loft to 400mm (2 x 200mm crossways). Then in the rooms below, paint the ceiling in tough paint, like Duracoat, or kitchens and bathroom paint. Those modern tough paints are pretty much air/water tight.

The problem I see with a sealed attic, is during the winter time, the chances of freezing water pipes and burst pipes, is highly possible. Its the movement of air through the rock wool and into the attic that prevents this.

I take it, boarding out the loft with chipboard is a bad idea? Will the boards cause moisture build up?

Hi! Great video! It was very informative and that PDF the lady made was very detailed. I was planning to the same to my loft with one slight change to her idea. So, vapour barrier on the ceiling side but rather than an air tightness layer on top, causing problems you've mentioned, I was thinking to use a breathable membrane. I believe the benefits of this system would be 2 fold. 1 to allow any creaping moisture passing the vapour control barrier to dissipate into the loft space and 2 to reduce or eliminate potential wind washing making the insulation that little bit more effective. My logic behind this is ive taken the suspended floor insulation method and reversed it. Does this sound at all plausible or am i barking up the wrong tree? p.s. Plan is to install a MVHR system and will be using rockwool in the loft and suspended timber floor, especially after watching this vid! Thanks

Thanks for all your videos Steve. Assuming you've got the nhbc 7.2.15 recommended amount of good back and fourth ventilation above the insulation, in a cold roof, do you think 50mm continuous air gap in the rafters is enough when there is old non breathable sarking felt, =>300mm of open air insulation, with no seperate vcl, above a shower room? Many thanks

thanks for your advice

On your way Steve - loose fibreglass insulation laid over joist (150-200mm) with air gap under eaves/tiles to allow air flow up and over- is it also ok to add kingspan to the underside of the tiles/felt (new roof) I've got 4 roof vent tiles installed to allow air flow - just thinking belt and braces or is this wastage material adding the kingspan

She is obviously a case of a little knowledge is dangerous. The air pocket we used in Texas for radiant heat reflection on the outside of buildings, it's not brilliant for internal insulation. This lady would be far better served with Rockwool insulation to let the moisture out and forget about PIR entirely. It's fine to have around the majority of down lights where PIR isn't and it's hydrophobic. Possibly she would be better served watching some insulation videos on The Build Show Network or Matt Risinger's YT channel as her document is trying to hybrid US and UK systems for insulation and vapour management.

Thanks - great video. A question please. I have the old felt bitumen type barrier under my tiles as you show here (around 9.30) in your summary. Can I just cut out what I can see, either all or sections maybe, and place the gas permeable material in its place (ie I'm hoping all the roof tiles dont have to come off - I'm just looking to assist with the loft ventilation due to condensation build up. Thank you for an informative video

I’m lost. Are you saying not to use PIR in between ceiling joists?

What about thermal bridging? Would the vapour condense in the rock wool without a vapour barrier?

Hi , just to ask , i am refurbishing the roof of our 1 level house extension, where before used to be shower , we have VAPOUR barrier on the plasterboard, as right now we have only toilet over there, my question is ! to keep that vap barrier or remove it ? thank you. we need that space to be nice and warm thank you

For a warm falt roof construction, could you put the vapour barrier on top of rafters, then osb , insulation etc?

Hi Steve, regarding moisture passage through Gyproc ceilings, as my ceilings are still 70s with Artex would this make a difference to the passage of moisture through the Gyproc into the roof space? Hope you can help.

Hi I live in a downtown stairs apartment and my kitchen ceiling keeps sounding like it caving in but there is no damage in my apartment nor the upstairs apartment. This sound first happened this Sunday October 30th and today November 4th

Hi Steve having a flat roof fitted. But which is the better. Epdm owl lava 20 or grp. Its a 4mtr x 5mtr it's a cold roof due to hight restrictions thanks

Mine was a nitemare (100yr old house). Put tape on hatch to seal and felt vents

Steve no sure of the best way to contact you and ask for some advise but l need to repair my flat roof as it wasn’t constructed properly in the first place, basically it’s a cold roof with no vapour barrier or ventilation, it’s about 12 years old and to put it politely it’s a bit spongey . It also has access to and upstairs flat so is walked on regularly, watching some of your videos lm thinking l would prefer a warm roof solution, even though it would cause me some issues with one doorway , cold roof is possible but as you are aware I would need to put a lot of effort into the ventilation design. Would love to know your thoughts on minimum fall and what material you would recommend for the top , many thanks

Great video! What about chipboard or OSB flooring which has been fitted over the insulation? How permeable is that?

Do all Victorian houses (late XIX) have roof eave vents or at least gaps for ventilation purposes? Looking from outside my roof seems to end really close to the walls.

Hi Steve, what is the best insulation board to use on the market for hybrid roofs? Thank you

What are the things called. That fir in the roof to keep the air flowing ?. Thanks

Not directly related but in the uk for cold roofs we now need to have insulation under the joists. So where does the vapour barrier go in this situation? Does it get sandwiched between the insulation?

Looking at a similar situation in my 1910s terrace. Difference is there is already about 3cm insulated plasterboard that was overboarded. I’d prefer not to take everything off for a vapour barrier. So curious: 1. Is it ever okay to put a vapour barrier over the joists but under the insulation in between them in a cold roof situation? (As in the diagram in the video) This seems iffy to me as could trap vapour on the joists. 2. I’m guessing you’d recommend rock wool or similar, but given there’s two layers of plasterboard and some EPS could I assume it’s fairly vapour tight anyway, and use PIR for higher performance? Thanks.

So fluffy stuff the rafter and use sarco vents. And dont use foil back on the rafters

Doesn't let air out but lets gasses out?... Air is a gas... The foil insulation is surprisingly effective with an air gap either side. It can be achieved by putting a baton on, then your foil layer, then more batons.

alright, I'm dying to know why this came up in my feed.

That lady should just watch and copy the steps in Matt Risingers video “Insulation 2.0”.

Lots of fluffy insulation = unusable roof space and cost of replacing every 10 years as it degrades go for a warm roof.