Warm Roof Firrings where do they go? Your Questions Answered

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If you need help or advice, alway call or drop me an email
07802300099
steve@londonflatroofing.co.uk
First, what are Firring (furrings USA)? in a flat roof, they are strips of timber or other material used to create a fall or gradient on a flat roof. The purpose of introducing a gradient with firrings is to allow for water runoff, preventing water from pooling on the surface, which can lead to leaks or structural damage over time.
The question from this viewer was where to put them and I'm often asked why can't they go on the top, especially when the old flat roof is to stay in place to be used as an Air Vapour Control Layer (AVCL).
As I explain in this video, creating an air void above the insulation could allow the opportunity for moisture to build up and then cause interstitial condensation in that area. Interstitial condensation is basically moisture in the air turning into water change of state and then soaking into the timbers and causing problems like mould or rot. So it's considered to be bad practice to place the furrings at the top and should always be fitted at the bottom.
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Steven Dickinson
London flat roofing
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info@londonflatroofing.co.uk
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Опубликовано:

4 ноя 2023

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Комментарии : 46

@SteveRoofer 8 месяцев назад

Please feel free to email or call if you need any more information or help steve@londonflatroofing.co.uk 07802300099

@kevinrae3299 8 месяцев назад

Thanks Steve, I’m a flat roofing contractor in NE Scotland, I only install warm flat roofs , but your videos condensation were excellent and helped me understand this better 👍 What flat roof membranes are you installing in London?

@SteveRoofer 8 месяцев назад

Mainly EPDM glad to of been of help. are you insulating at the fascia?

@kevinrae3299 8 месяцев назад

@@SteveRoofer depends, a lot of my wood designed by architects, so sometimes. I’m currently doing a job that’s been specified with 250mm pir ! Do you reckon after 150mm there is any benefit? I have my doubts?

@9111logic 8 месяцев назад

From what we've learn from you in the past the answer was pretty obvious but thanks for the refresher 🙏

@SteveRoofer 8 месяцев назад

Yes, I'm starting to repeat myself because most of my videos are 10 years old, I can't believe it

@miantamoorsaleem8287 7 месяцев назад

Please make some videos on warm pitched roofs, or where the insulation is above the rafters. Great channel 👍

@SteveRoofer 7 месяцев назад

Yes, I have some more warm roof videos coming shortly

@richarddicktaylor219 8 месяцев назад

Thank you for such a comprehensive explination

@SteveRoofer 7 месяцев назад

You are welcome!

@voodoomotion5855 2 месяца назад

Hi Steve, we are building a truss roof pitch 22.5, unfortunately we're in an area surrounded by squirrels and field mice 😀 how would you recommend creating a warm lightweight roof covered with tapco or eco slate? I noticed some people putting batten over the rafters to fasten the insulation in place, then breathable membrane and horizontal batten for the slate. However i'm worried about critters getting in. Would it be better to fasten OSB direct to the insulation, cover with breathable membrane and tapco without batten? I know with a flat roof you have to be careful of the screws propping up through the membrane, but wondered if it's ok with pitched? Really appreciate your advice, cheers!

@user-zu7no9md4t 2 месяца назад

what for is bottom osb board? is it possible to lay insulation boards straight on beams?

@cbdtribe398 4 месяца назад

What can be done if no firring strips have been used in the first instance? And the roof has been constructed. Basically my builder has left me hanging and disappeared with my money. The roof was constructed using warm roof method, joists, osb, vapour barrier and 150mm insulation and OSB again. And he's since done a Houdini act. However there are no furring strips visible and slope. Please advise on a solution to fix this without having to rip the roof down. Thank you Steve.

@NeonXXP 8 месяцев назад

I intend to use Easi-Joists that overhang a timber frame to create a warm roof on a single storey annex. Any advice on insulating in-between the Easi-Joists at the top where the wall insulation and roof insulation do not meet. I have some 75mm PIR to fill the main gaps but Easi-Joists have a metal skeleton frame that would need to be packed out somehow. I have considered rock wool or expanding foam, is there any sort of common practice?

@NeonXXP 8 месяцев назад

I think I might be able to answer my own question. I should ask for solid timber webs where the joists cross the wall plate to allow for insulating.

@lozmoore1312 6 месяцев назад

Thanks for this. How is the top osb layer fixed down and butted up to each other? Thanks

@SteveRoofer 6 месяцев назад

you screw through using thermally, broken fixings and pull it all together make a really nice sandwich

@AndrewHelgeCox 8 месяцев назад

If the top of the roof develops a hole, does the vapour barrier act like the tanking on a wet bathroom and trap all the water that gets in, eventually filling up any gaps around and between the foam pieces? I'm assuming a closed foam which doesn't act like a sponge is used to minimise this?

@SteveRoofer 8 месяцев назад

Yes, basically you will have a swimming pool when the insulation gets wet, it is useless and the whole thing would need to be stripped. This is the big big problem with warm roofs. This is why they have to be done so well and looked after. Otherwise they are going to fail and cost a lot of money to replace again.

@builderNorthamptonn 5 месяцев назад

Cause the problems now arise of 150mm insulation and that will only get bigger . Cause and effect being bigger screws and facia boards that will soon look like advertising boards 😅

@Jackzuk 7 месяцев назад

Can you see any issue with putting the PIR direct onto the joists. My builder has done this, put osb on top and then edpm. Its a timber framed loft room and the roof parameter is all parapet. I am worried about the lack of a VB, just foil on the pir. Would installing a VB between the plasterboard and the joists cause more issues. id even go as far as stick alitrix to the underside of the joists but worry heat wont pass through it a making gap between the joists colder. If so could just use a visqueen one

@SteveRoofer 6 месяцев назад

You can't do it because you've got nowhere to lay your air vapour control layer that should be glued or torch down onto a board. You can't successfully use a plastic sheet are vapour control layer without having boards either. Also, it makes the roof a little bit bouncy so realistically it's not a very good job.

@anonay7238 4 месяца назад

@@SteveRoofermy builder has done this in my loft dormer too. Roof joists-> firings-> PIR-> OSB->felt. No vapour barrier to be seen. Hope I don’t have issues in the future but looking at your videos I’m due a hefty bill in a couple of years. Although on one of your videos I did see PIR on joist (no osb/vapour barrier) and you didn’t point it out specifically.

@vaper106 7 месяцев назад

Can you tell me if there is any reason I can’t drop the bottom decking down between the joist if the moisture barrier follows the contour. IE I’ve 9x2 joist and and was playing with putting deck half way down giving an extra 100mm insulation. Space would be tight to get 150mm insulation above with a good fall. I appreciate its more work but could I. Thanks. Enjoying the vids

@SteveRoofer 7 месяцев назад

You're always best to drop me a drawing, so I can have a look because that's hard to understand

@kevinrae3299 8 месяцев назад

A few manufacturers I’ve done specifications for say that by using ply/osb directly on top of insulation you are creating a cold roof and don’t recommend doing this . I doubt in reality it’s a problem, maybe depends on if it’s fully adhered or mechanically fixed membrane?

@SteveRoofer 8 месяцев назад

Well, you are definitely not forming a cold roof, but actually one has to question if you should use Timber over the top of the insulation be OSB or ply. Realistically it is something that is inside the sandwich that could rot if there was a problem. Trader the organisation that deals with timber products is totally against it and personally I can see lots of merits for not using any Timber products in the sandwich. I have placed EPDM rubber and felt directly over the top of insulation before and never had a problem.

@DICEGEORGE 8 месяцев назад

but we want to dance on the roof ! so from below: beams, osb, vapour barrier, kingspan, vapour barrier, osb, epdm ? @@SteveRoofer

@anonay7238 4 месяца назад

@@SteveRooferSteve, this reply is a bit contradictory to one of your other reply’s (that I comments on) where you told a chap his builder (and mine, since he did the same thing) built him a naff roof because he left out the bottom osb and vp!

@tonyclarke8224 6 месяцев назад

Your decking board on top of firings, Vcl and then insulation

@markstipulkoski1389 7 месяцев назад

I'm not a roofing expert, but could your roofing recommendations be focused towards your particular climate? In very cold climates like Canada and the northern US, I've seen a ventilated air gap between the upper roof decking and the exterior insulation. It is used to prevent ice damming. The concept is that the the upper sheathing is even further insulated from the thermal mass of the structure and therfore quickly assumes the ambient temperature and therefore the snow doesn’t melt and later form ice. In hot climates, like here in Florida, the surface of the exterior insulation typically has a reflective radiant barrier which requires an air gap above it. Basically, it keeps your insulation in the shade.

@SteveRoofer 7 месяцев назад

Yes absolutely we are in a cold wet climate. If you're coming from the US then you have lots of different regions in warm regions which are moist you put the vapour barrier on the outside where we are we put it on the inside so it is quite complicated and you really need to make sure you know where you are and what conditions you are in.

@un7ucky 6 месяцев назад

something to note is that those are always vented out the top and bottom

@stevenm9067 6 месяцев назад

Due to have my flat roof replace in the spring. So will give me questions to ask the surveyor when he comes to measure up.

@SteveRoofer 6 месяцев назад

Glad to have helped

@DICEGEORGE 8 месяцев назад

does the red vapour barrier go on all 6 sides of the PIR? ontop and around. with some kind of tape?

@SteveRoofer 8 месяцев назад

Yes you need to make sure that the Air Vapour Control Layer (AVCL) is airtight and no air from inside the the rooms below can get up into the warm roof.

@fghjjjk 8 месяцев назад

Are there any considerations regarding cold / warm etc in a standard house apex roof?

@SteveRoofer 8 месяцев назад

Yes building regulations actually states dont do a cold roof unless you have to.

@SteveRoofer 8 месяцев назад

this is a quote from BS 6229 page 28 It states that "NOTE 2 This type of roof is not now recommended." This is because of the difficulty of forming and maintaining an effective AVCL below the insulation and of providing sufficient cross ventilation above the insulation.

@fghjjjk 8 месяцев назад

@@SteveRoofer bs6229 is for flat roofs with a pitch no greater than 10 degrees. My question was for a standard pitched roof. Regards

@paulfaulkner4488 15 дней назад

You are mentioning a vapour barrier just use the right insulation with a multi foil

@rockyrowlands3652 5 месяцев назад

But doesn’t wood naturally breathe ? And any vapour dissipate via breathable membrane under the slate .

@SteveRoofer 5 месяцев назад

Wood is not a very good vapour barrier and we'll theoretically allow vapour through. However, men made wood has glues in it that retard the amount of vapour that will go through.