Flat roof design going wrong. Who is responsible for your flat roof design?
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- čas přidán 7. 09. 2024
- Who designed your flat roof? The Builders, Roofers, Architects, Structural Engineers, an agent? Confused? Any design shoud be detailed and have all the drawings and specifications so that the builder can build with confidence. Unfortunately, it appears that this is seldom the case. Most drawings or plans I find on site have just enough details to get the job through planning and building control; design details are just not there. This becomes very apparent when it comes to flat roofs and vapour control layers. A basic generic drawing is shown with some written details next to it. If you are lucky, the mention of a vapour barrier will be there but not what type. Roof insulation thickness is often there, and a supplier's brand name. Often different brands are used as they are cheaper than those specified. I think I know the answer, but I'm going to keep it for another video.
The biggest problem I'm finding with new flat roofs in London is, after two or three years, the decking is rotting from the inside out. Black mould, fungus and rotting timbers are all to be found once we open up the roof and do an inspection. This is found on large and small flat roofs; flat roofs that have been designed and overlooked by teams of engineers, architects and surveyors. I think we have a ticking timebomb on our hands; the more we insulate our houses and buildings the bigger the problem gets.
Link to video of skylight being fixed
• How to build a insulat...
#steveroofer #coldroof #warmroof
You've hit the nail on the head Steve, who should be responsible for the design ? With ever more complex roof designs and associated products it's invariably left to the builder/chippy to come up with the "right" solution and we're not really qualified to do it. Most working drawings show absolutely no details at all .
A good builder should know this, it’s actually very standard stuff. It’s the difference between a good knowledgeable builder and someone who doesn’t know or care enough. You get what you pay for and good quality building work is expensive. The upstand details are fundamentally the same on all jobs, vapour barrier, continuous insulation, ventilation if necessary, correct application of all the above and there won’t be any problems. I always enjoys your videos, detailed and informative
I am glad to see that a tradesman understands his trade. There is so much **** on You tube by so called builders that maybe CZcams should take down fake and misleading content??
As regards your question concerning the detail: It should be the designers responsibility to detail and specify the materials to be used, be that Architect (I am one) or surveyor etc. Small builders are invariably a tradesman who has set up to install all trade elements, I've met several builders who are say, a brickie by trade and confess to knowing nothing about joinery or decoration relying totally on their subbies, who just want a quick in and out and get paid.
As regards the detail you show, I assume that the ceiling is still to be installed, then the vapour barrier can be fixed to the u/s of the joists all with taped joints and taken up the rooflight cheeks. The plasterboard is then fixed through to the joists.
BTW your example of the VP on a roof shows a very thin piece of insulation to the rooflight cheeks that also does not have a structure for the rooflight to sit on. With that form of construction I would expect warm moist air to accumulate under the rooflight and condense on the poorly insulated cheeks. Also the plywood would deteriorate with the moisture causing a decoration mess.
Always found that insulation causes more problems than answers look forward to part 2
To answer Steve's question, I'd say the client is ultimately responsible. Depending on how they commissioned the work, that will determine who has the delegated responsibility. Chances are, the client didn't use an architect and has gone straight to the builder who's given them a price for the full scope of works. If that's the case, then it's either the main contractor or their roofing subcontractor who would be responsible for the competent and compliant design, depending on the nature of their 'contract'. If any deficiencies haven't been picked up by the BCO, that doesn't absolve the specialist (sub-)contractor from building a robust construction.
I'm all for insulated upstands, but the size of that rooflight/lantern opening is far larger than the other version shown in your own video. I dare say that if the 12mm(?) plywood upstand isn't up to much abuse from a knock or a kick at some point in the future. I think a SIPS style upstand would be a better approach myself to get a circa 75mm wide upstand. Some rooflight manufacturers offer these as 'bolt-on' options when buying the rooflights/lanterns.
It depends on the job requested in terms of who should be defining what to do? If the builder know what they're doing and accepted the job with warranty, and the client knows what to expect, the leaving to the builder is fine. If not, a subject matter expect should be involved.
I think the architect is responsible for how the upstand is built and insulated. Same with the flat roof constuction. Even if we know how it should be done. If the architect wants to put a skylight so close to the wall let him tell us how he wants it weathered. It happens all too often. Same when they put a loft dormer 300mm away from a party wall. Good video.
A detailed drawing showing how to construct the upstands would go amiss. Now If you know that and I know that why isn't it happening?
I agree there should have been a detailed set of drawings given to the builder. Too many Architects are doing cut and paste details that do not carry the right info these days.
When the new building regulations come in later this year I think a lot of this will stop
I am a GRP roofer i tell customers all the time they need a vapor barrier on thir build mainly cold roofs as warm roof its my job to do it and the amount of times they come back to me an tell me the building inspector says we dont need 1 is unbelievable,, they all have new builds with fancy pods but put spot lights in the ceiling carnt work em out ,,
Any builder should have the knowledge if the work they take on. I am personally fed up with people doing work like this. I now build garden rooms and the amount of apparent professional companies who build a sub standard garden room from a design aspect but looks good. Most are doing a cold roof with no ventilation.
There's quite a few companies doing this. Oakwood garden rooms on youtube do hybrid roofs where the PIR insulation is pushed right upto the OSB. They report no problems so far.
they are all trying to get insulation into their builds at same time as meeting PD regs. Are you building under PD regs and managing to ventilate still?
Shouldn't the upstand be built straight onto the joists and then insulated in-between?
Hi Steve, could you give me a bit of advice. I am building a garden room and the roof joist are 120 x 45(5x2). I was thinking of using(cold roof inside to out ) 12mm plasterboard - 1000guage polythene - 25mm PIR up to joist - 100mm XPS insulation between joists and 20mm air gap under decking with continuous soffit vents back and front. will I get problems only having 20mm air gap
The problem is UK gov doesn't regulate the builders. Anyone can rock up in a white van and claim they're a builder. Before you sign up make sure you know them and they've been in business for 10+ yes ask to see their accounts that scares the shit outta them
The problem is builders dont go into the detail nor is the material or design anywhere to be found. There should be a good practice guide.
I mean NHBC have freely available standards, they're pretty decent overall if not perfect. So there's no excuse. Too many cowboys
Hi Steve, thanks for your informative videos, would you be about to post a tutorial of how it should be done from start to finish?
Next time I do one I'll make sure I video it from start to finish but have you seen this one czcams.com/video/f5Ixyb-2CHc/video.html
Thanks, I will look forward to it.
Devil in the detail, don;t leave spec to the builder, project manager should ensure detail before installation of windows, someone should be linking up between chippy and roofer/ flat roof installer, every design is slightly different, but excellent warm roof build up Steve
A much better way of building these lantern opening is to take the extra time to construct a four frame of a triple which is within the ceiling opening value. Lot more space to insulate, get your vapour layers in and stops cold bridges. Easy to keep your opening square too
Yes that's the way I do them
What do you mean "a four frame of triple"
I'm about to construct a warm flat roof with a central lantern and worried about the lantern upstands. Can you explain how you do it in more detail please.
Thanks 👍
This detailing is far too specialised for your average (or even above average) builder. I'm sure the builder thought that they were doing the right thing but vapour is sneaky and unintuitive. Water flow shingling is about the extent of a builders scope and that's as much as I'd expect from them.
Manufacturer or architect prescribed detailing is really needed.
The problem is there's no book to reference too.
For building regs you have to prove that its fit for purpose and ticks some boxes.
Give a builder accurate extensive drawings and your good to go.
If you don't have a drawing you can't say" that's not what the drawing shows"
If you think the builder will sort that or get over that then that's what they'll do.
Good luck getting a builder that's been in business over ten years that'll show you there accounts 🤣🤣 your hilarious
The material used should have been specified along with the drawings.
Foil backed plasterboard? I think that's what it's for
Hi Steve, the information I've gleaned from watching a few of your videos is amazing! Thank you so much for sharing your knowledge. I'm a residential home owner from North Essex. I'd love to upgrade the insulation in my existing 30 year old flat roof extension which otherwise appears to be absolutely sound. From your videos I've worked out my extension roof is currently of cold construction but there are no physical obstructions or height restrictions requiring any upgrade to also be of a cold construction. But I'm very wary of causing any structural problems as a result of employing someone who doesn't really know what they're doing. Do you have any advice as to how I go about finding a roofing company local to me who I can be confident will know what the correct approach would be?
I find that after talking to different roofers I slip in the conversation details on warm and cold roofs. I ask what VCL they use. most of them give the incorrect answer. Another one is to ask how you vent a warm roof. You Don't shoud be the answer.
how do you install and waterproof a skylight on an existing torch down flat roof
Hi Steve I can’t find the link for the other video you mentioned.. could you send it ? Thanks Gareth
i was looking as well
Hi Steve, I'm in the process of building a flat roof for a newly single storey. The plan was to have a parapet wall with allutrix over the sub deck 150mm insulation and finishing with resitrix full bond. Things were a little sloppy with the structure engineer/ lintel, which led me to change the roof layout into a traditional(not parapet). Is the mineral felt ( torch down) method my best option or can I still use resitrix? Thanks
You can use torch on felt as a vapour control layer if you want. However it has to be one of the thicker torch on felt personally I don't use it but I have seen specifications that one or two layers of felt will work as a pair of vapour control layer. The main thing here is to think about the air control of the system. The torch on felt over the decking and up the walls if applied correctly will be 100% airtight and actually that's probably more important than the vapour resistance of the product.
It's all pretty simple actually. Builders have to follow the Architect, Structural.... and so on Drawings. If they change the drawings then the liability lies with the Builders then. So, whatever is wrong on Architect or whoever's detailing is done for the builders on the drawing, those are responsible for the mistakes. Meaning Architects should have learnt better in universities. ;) That's all. However, this case is not the worst one. It can be easily fixed at this stage. Since the roof is not covered by GRP or Epoxy Resin...yet.
Yes that pretty well sums it up
Most small builds I see don't have detailed drawings, they rarely tell you the brick and block type let alone build specific details.
They expect the builder to use experience and the builder asks the home owner if they have queries.
There should be simple to use resources that details all the simple common issues, instead you have to search multiple
Thanks for the great video.
Does a cold flat roof need vapour barrier?
Yes it does
Can you tell me what insulation values the expanding foam you keep using give us and where your buying one that gives any values at all, you keep having a dig at other peoples work , when your doing it just as bad, relaying on a tin of expanding foam to fill pore cut gaps in insulation, yes it’s better than nothing, but let’s be fair, it shouldn’t be used and any good building control officer would pull this as gaps shouldn’t be so big when cutting the insulation boards, personally I wouldn’t take great pleasure in pulling somebody else’s work, it’s easy for anyone to do that,
All U values for the insulation we use and for all insulation will be supplied by the manufacturer
I think foam is wonderful stuff tbh
Hi Steve, would it be possible for me to email you a quick sketch of how im planning to construct my warm roof, which includes a lantern? I'm a bit a worried about getting the vapour barrier and insulation wrong.
Thanks, Joe.
Yes not a problem just email over
@@SteveRoofer thankyou, whats you email address please.
@@joefowler9600 it on the top of all my videos info@londonflatroofing.co.uk
@@SteveRoofer thanks Steve, I've just emailed a quick sketch 👍
Hi Steve, I'm having an issue with my roof lantern upstand insulation. Ideally I would like a proffesional to take a look at some photos to see how I'm going to get over a problem.
No where local to me knows what they are doing when it comes to warm roofs
Thanks!
Do you have an email please for your advice? I understand if there's a charge
email me over some details steve@londonflatroofing.co.uk
Builder builds things a desghner designs things simples , agreed in what you have said, makes sense
But BCOs and desighners ,colleges need to educate us more on this area , ive done both methods , never had a problem but technically your right , lots of things here that rattle me condensation being one if a board is put on the deck will it just decay from condensation , bco by me telling lads to roll dpm over the roof 🤔 dont seem right could be a condensation trap also used alutrix
Quality advice
I currently have a conservatory with a glass roof 3.5m from back of house out. I want to put a flat roof on with 2 flat sky lights. Will I need planning permission to turn a glass roof into a solid flat roof?
Yes probably you need to ask the planning department
@@SteveRoofer thank you I spoke with them today and no building regs are required. What thickness osb do you use for the bottom deck and thickness of osb if you are boarding on top of the celotex thanks Steve
Can I ask what the detail would be for a roof created from sips panels?
Depends on the makeup of the sips panels. f you are having panels made they shoud have been made to a specification that works. If there of the shelf perhaps email me some details and I'll see if I can help
Don't need a vapour barrier on a warm roof construction. I would never put a window load on insulation. And they have point loading here too. The insulation does not seem thick enough to comply. It should be 150mm if it isn't.
The flat roof Insulation should be as thick as necessary to get to the correct U value for building control this is taken as an avage what we don't know is if its not thicker elsewhere. Yes you do need a VCL with a flat roof. I don't understand the other comments please elaborate
@@SteveRoofer this is a warm roof construction which negates dew point but the foil is built in to act as a vapour barrier and if they thought this they were correct - unless you know something else which I'm open to hearing. Regs change all the time as we know. You are correct it has to be thick enough to comply and compliance in this case is 150mm unless there is insulation below. I think it's to achieve a 0 .2 wm2 U value. Building control may ask for a venting membrane over the insulation but this is not required in the approved documents as far as I'm aware but due to the love of private companies by the Tories they have opted to use NHBC standards which go unnecessarily into greater detail . NHBC only do this so they can avoid the scrutiny of local authority which allows them to self inspect on the strength of its standards. The organisation is funded and originated by house building companies. I refuse to work to their standards when BC try to inflict them on my jobs and I refer the officers to the Approved documents when I re-buff their NHBC assertions. A venting membrane has no use whatsoever here as it has no moving air above it and is sealed in.
In terms of point loading there is.firring strips below the insulation which when weight is applied would cut into them causing depression and deflection in the plane of the flat roof the screws pull the upstand frame down. Under a concrete floor the boards spread the load of the concrete and the live loads imposed but in this case the weakness of the insulation boards could prove troublesome.
I'm an Architect with 20 years experience and agree with everything said in this video. You always need a Vapour Control Layer with a flat roof as this prevents interstitial condensation at the dew point of the roof - ie usually within the insulation layer. Warm air rises and usually with moisture. When this happens you'll be compromising the insulation and may cause damage to the building fabric. The foil on the insulation cannot be relied on due to the termination points being in the wrong location - as outlined in the video. The VCL needs to terminate higher and be continuous under all insulation panels and around penetrations.
@@freemarketiconaclastbastar4297 Don't be daft, of course you need a vapour barrier. Given the average UK temperature fluctuations, the dew point will occur nomatter where you have the membrane, you just want to make sure it's happening *outside* the VCL. You can't change the laws of thermal dynamics. If you go from say 21 degrees internally to say 5 degrees externally, the relative humidity of the air cooling as it goes through the wall construction increases. You just need to give your wall make up to Kingspan (or other major insulation manufacturers) and they will calculate and send you back a graph showing where in the build up the dew point occurs. I think you're getting confused with breather membranes perhaps.
@@giotto4321 No you do not need a vapour barrier, it is not required by building regs. In a warm roof construction the dew point does not occur within the roof's profile and the foil acts as a vapour barrier anyway. That is the point of a warm roof.
What vapour barier would you recomend?
ALUTRIX 600 Self Adhesive Vapour Barrier
You can use dpm visqueen 300mu 1200 gauge.
Perhaps over confident newbies.
Too many mixed points in the comment - you don't need this you don't need that etc etc. In that case no1 has a clue. Too many cow boys
I blame brexit
Too many cowboys around... too much of a “it will be alright” attitude - worked with too many semi-skilled roofers myself.
Technical details should come from passed experience jobs, any additional/specified details should be from an architect drawing.
You get paid for what you know.
Yes we are really running out of skilled workers fast. Two decades of no parentship and limited training
What a load of crap! I have always said a little knowledge is dangerous
You are kidding arent you ,you dont need a vap bar to the sky light detail
Steve your talking rubbish. All depends on the type of grp as to the roof construction