Great explanation of "thermal siphoning" - most of the houses here in Ukraine have no insulation, so the little house we bought got an upgrade - first the ceilings got two layers of rock wool, about 30cm, then the sides of the house were covered with 10cm foam and stucco, then I extended the roof by one meter all the way around, so I could wrap the corners with foam and cover it with under roof rock-wool. There are no cold spots, therefore no condensation. For winter windows I added a third layer of clear plexiglass with wooden frame to the outside of the double glazed windows. Little condensation around the glass edges in the kitchen and bathroom. Sure keeps from sending gas money to Putin. Love to watch your videos, you get to the point without much ado and tell it like it is. Thought about heat pumps, watched your videos and will hold off. Best investment were some solar panels, a low frequency inverter (6KW) along with 800AH LiFePo batteries - reduces my utility bill by half, except for winter months. Thanks for your videos!

@MargotDobbie

2 жыл бұрын

"Sending Gas money to putin" . Without Russia you would have no Gas. Cant wait for you to be humbled when they invade lol

@g7vqedave2

2 жыл бұрын

@@MargotDobbie Yep, thank Russia for allowing people to carry on warming the whole world by still burning gas.

@michaelcoles6140

2 жыл бұрын

@@MargotDobbie how do you find an invasion funny! Russia just wants to flex its muscles but will soon realise it has only just started to get muscles and will full within weeks… funny how you go by mindful but are just mindless…. Hope you don’t get run over or anything and can live in peace you complete idiot.

@normanboyes4983

2 жыл бұрын

@@MargotDobbie A rather unthoughtful reply. When Putin invades Ukraine - what do you think will happen to the energy spot markets? The answer is the price of gas will rocket and unless you are 100% off grid and grow all your own food you will be 100% impacted.

@justicecase19

2 жыл бұрын

Mindfull, hmmm I'm assuming your name is ironic.

Perfect timing! Roofer asked me today if I wanted to retain the parapets. He explained the situation exactly as the video. I now feel knowledgeable.

I knew nothing of parapet walls. Although I have seen them I never knew the nomenclature. You pointed out some very informative problems. Thank you. 👍👍

I have a couple of neighbours with the same story. First the roofer replaced the leading (sloping warm roof with parapet) then new coping, still condensation. Massive job to fix, so they have to live with it.1960s build, so originally it did not have heating. Cavity wall retro-fill. You have nailed the reason.

Great demo. Absolutely gem of a video. I wouldn't of learnt anything today without that video👍👍. Top man rodge.

That's a clever way of solving the issue, similar to my old builders which follow Joe Lstiburek's building science "perfect wall". As long as the Water > Air > insulation barriers are all joined and layered in that order it minimizes and in most cases removes the issues.

Absolute Genius. Many thanks for that clear and concise explanation.

Excellent stuff! I've been a plasterer, tiler, plumber, electrician and carpenter for many years now and consider myself to be experienced, talented and knowledgeable but I still learn something new from all of your videos. Keep up the good work!

Great video and explanation. I'm building my extension now and am debating going with a parapet vs not. The top will be a walk out balcony so I figured the parapet would act as a nice bit of privacy from neighbors. The points you make about straight walls and how they are great looking when they're first done but over time they begin to stain and other problems are created, I could not agree more, I see this all the time in Brooklyn. I do like the overhang roof because when it does pour you do feel a sense of relief knowing that the water isn't coming straight down as soon as you open the door or running down the wall. That sense of relief is reason enough to go with an overhang versus a parapet.

I just love Rogers humor! As always a good video, educational and funny.

it all makes sense roger, you've got a knack of explaining things so that anyone can understand them

Really great video to better understand the vast world of parapet walls. Many times in my life I’ve tried to make some quality parapets, unsuccessfully. Now, with your great explanations, i will be able to do so. Again, thank you very much. I Love you Roger. Deeply. I would like to feel those steady hands on my body.

Roger is correct about taking insulation up the parapet wall, I always make sure I take the membrane up , over and down 20mm . So as the roof is water tight without the cope/capping.

@BerkeleyTowers

2 жыл бұрын

Yep, absolutely agree... I closed the parapet wall and applied exactly the same treatment to the parapet as the actual roof ( in my case a liquid membrane). In theory, I shouldnt need the coping at all, but if course it's a big design aesthetic point. But crucially, the coping is only the first line of defence....... not the only one.....

I've really learned something today Rodger and will be using this if I take on an extension like this, keep up the great vids😁👍

Thanks for sharing your knowledge and opposition on this subject 👏🏿👏🏿👏🏿

That is a great solution, very well explained, thanks Roger.

Roger, thank you so so much, you have given me a lot of inspiration and key things i need to take into account when designing a parapet wall for my Masters in Building Surveying coursework!!

It needs the insulation standing up on the inside of the parapet wall and then the roof membrane covering extended up and under the Cap stone. Will require extra width on the cap stone to accommodate the increased depth of the parapet. Excellent rant Roger.

@peterdallyn6440

2 жыл бұрын

Totally agree, a lightweight stud wall would work but if timber it'll start rotting pretty soon. Plus the outer leaf of brick is supported on a very weak element, probably not an issue if the parapet wall is low, but if a reasonable height it would be quite weak. I agree to keeping the inner wall in masonry, but adding an Insulated upstand behind the single ply. Rogers point is really well put though, this detail is so often overlooked by designers \architects.

I like your solution Roger and it's pretty much how a competent Architect/Designer would normally detail it. In Australia we don't have as many dampness condensation problems as you have in the UK due to our warmer climate - we certainly have them but not as often. Over here, concrete roofs are not all that common, we certainly have a few parapet walls but usually in conjunction with metal deck roofs. Before I retired I worked in the Architectural profession and I have detailed many parapets in my time. I am pleased to say however, that I can't think of a single instance where they gave a problem. I would say that trying to flash into the face of brickwork at a DPC is always fraught with danger and we always detailed our parapets with the roof flashing carried up for the full height of the parapet and over the top and almost always in conjunction with a stud frame as the inner part = exactly as you explained.

Excellent as always. Last winter I found a leak into a shop in a 1970s property which no one had been able to trace for 25 years. Turned out it was because it was on a parapet edged slanted roof above an entirely dry flat above the shop. Despite roofers and architects and surveyors over the years it had never occurred to anyone that it might be the UPPER roof, not the walkway outside, which was part of the shop roof. Why? Because it was following the cavity down and bypassing the upper flat. leak was a combination of poor flashing and damaged tiles.

Your channel is the best building site on YT. Love it. You are a great instructor.

@SkillBuilder

2 жыл бұрын

Glad you think so! There is some good competition out there and we are constantly looking at ways we can improve.

I lived in a 60's low rise block, with a flat roof. This was a concrete slab construction, with brick piers. This was before expansion joints as well. The flat roof always gave problems for the top floor flats. Block spent a lot of money on re-roofing with a specialised covering. I did suggest that the block get planning permission for a butterfly roof constructed on top of the old flat roof, since the flat roof sloped to the middle where all the drainage was. But the block went for the cheaper option.

You hit the nail on the head, I'm going to renew and insulate my flat roof, and I was thinking how to construct the edges of the roof, in combination with exterior wall insulation. My idea from the start was to stay away from proper parapet walls, which means I'm not extending the inner leaf of the walls above roof level. My idea is to have a bit higher raised roof edges with insulation against the inside of the outer leaf which extends above the roof, the top is covered with a thick plywood sheet which extends enough over the insulation on the inside, and outside the outer leaf, both 70mm. The roofing membrane is covering all of this and finished with a trim piece. Zinc sheeting with rolled over edges is used to finish the top of the edging. This will give the idea of a parapet wall from the outside, but in a more classic way and without any cold bridging and leaks, as long as the fasteners for the zinc sheets are sealed well where they penetrate the membrane.

Very interesting Roger, when we had ours done we noticed almost immediately after the first heavy rain, water coming in to one side of the bifold doors, on closer inspection the existing rain water down pipe from the original hip roof that was now impeded by the extension was discharging onto the new flat roof but through an extended piece of down pipe now laying flat to the roof, massively directing the contents of the main roof rain water along and under the flashing. We are in a small terrace and three roofs collect into a joint guttering at my house. In future I’d do what you suggested to avoid the cold bridging and direct rain water either off the roof entirely or a small boot into the centre of the flat roof

Steve Roofer's videos are the absolute best when it comes to all things flat roofs. Great if you could get him on for a discussion on flat roof construction techniques.

@SkillBuilder

2 жыл бұрын

Great suggestion! We did ask the question some time ago but he didn't reply. I guess he is happy doing his own thing

Whilst I have no need nor likely never will need a parapet wall, this was a very good explanation of what to consider should I ever have the chance to have anything to do with one (hope not). Thanks.

Really, really interesting and well explained, nice one!

Roger is spot on again great video

Superb explanation, thanks for sharing 👍🏿

Great video, saved to my house design playlist for reference!

@SkillBuilder

2 жыл бұрын

Glad it was helpful!

Thanks so much for explaining this Roger! I've had this EXACT problem in the garage of an extension we finished recently and couldn't work out what the f#%king hell it was!!! Well at least I now know how to rectify the problem. Will be looking at this detail a lot closer next time when building / going through the architectural drawings. Cheers from Australia mate, Nick

Great instructional video

Great explanation Roger.

Great video. Makes perfect sense to put a thermal break in the masonry. Personally, I insutlate everything on the inside e.g. 50mm EPS under the plasterboard and XPS for the floors.

Thank you for your insight! Interesting topic! You are awesome Roger!

Interesting video. We built a large extension about 20 years ago with a parapet wall. It's still on its original felt roof and we never had any issues with moisture ingress. We keep thinking about replacing the felt because it's technically at the end of its design life, but we inspect it every summer and it's completely fine. I can't even justify changing it to GRP, since the felt has lasted so long. I think your opinion is a bit too harsh on parapets, but I hear you.

Good stuff. Glad you mentioned roof overhangs. The first thing I look at on a building is whether the roof overhangs the walls and how far out it goes. The overhang is an enormous asset in preserving the condition of walls.

@TheBrick2

2 жыл бұрын

Timber house in that harsh Norway climate have a good overhang and last hundreds of years, makes all the difference. Good hat, good shoes.

@TurinTuramber

2 жыл бұрын

Some bedded verges on the gable end only overhangs two inches. Must be lucky with the weather.

They've been the rage here Down Under for the last 20 years! So there's been plenty of leaks in that time, few guys know how to construct them properly and even fewer plumbers know how to flash them and sort out correct sized drainage. We don't/won't have them on our houses!! Keep up the good work Roger.

@master_Blaster91

2 жыл бұрын

Do plumbers do the flashings for roofs down under still ?

@68bwild

2 жыл бұрын

@@master_Blaster91 Yes in theory :)

Cheers Roger, very helpful buddy

Makes sense,thermal bridging in that area is easily missed,and missed diagnosed. Good video cheers

Excellent.....thank you !

Brilliant episode and great info. Just about to build a flat roof with a parapet funnily enough 😄

Very interesting and I have to say I agree with everything you said.

Excellent case study

Good opinion, I will use this when I build my house in the pacific, parapet walls are good for cyclone proofing.

nice solution Roger

Good explaining👍🏼

So right about stains appearing a few years later down the front of the building due to no overhang in the first place.

Agreed Rodger as a golden rule I always try to have all insulation over lapping onto each other, mitigating the cold spots where the ceiling meets the external wall insulation.

Always a great rant as usual🕺🎯

very knowledgeable nice one Roger

I’ve got that problem, we had Roy Rogers and Billy the Kid build our extension (badly as well) they took all the cash and don’t answer the phone now! At some stage I will need to get it sorted, but you are 100% correct in what you say Roger, great video as always, thank you.

Excellent illustration.

@SkillBuilder

2 жыл бұрын

I really need to learn to draw this year.

Well said. Great video.

Thank you for doing this Roger and the consensus view of the comments thus far is that you have nailed it. However, I am surprised that you did not consider adding a heat pump to sort out condensation problems. Taxi! 😉👍

@paulhaggett3710

2 жыл бұрын

🤣🤣👍

Hello from California. Good content. I'm used to seeing them built in commercial multi-tenant buildings and row housing developments, they're usually used as firebreaks between the units in the building by extending firewalls 2-3 ft above the roof surface to keep flames from jumping along a roof. I've never seen a house with them as a decorative element.

@MadRat70

2 жыл бұрын

They are not uncommon in stone mansions. That is probably an uncommon design in California.

Thanks for the video, nice explanation.

@SkillBuilder

Жыл бұрын

Glad it was helpful!

Good man thanks for the advice 👍

Thank You

Another excellent video.

Great vid again

Im well experienced builder but you have my thumbs up!!!

That was a very good explanation Roger. As a bricklayer I would like to add to this, the increased specification of concrete blocks rather than thermalite blocks. Yes they are stronger but they create a real problem with cold spots. Your example is a classic case, if the inside wall is made of concrete blocks the cold spot would be far worse than if the internal wall was built out of thermalite. I suspect dot and dab is also far worse than a light weight plaster too.

@deanmsimpson

Жыл бұрын

Do you believe thermalite blocks would stop the 'cold bridging' Roger speaks off? Therefore not needing to build the inner skin out of stud-work?

@harveysmith100

Жыл бұрын

@@deanmsimpson You would have to check with an expert in thermal values but thermalite blocks have a great thermal value. Many years ago we would build houses with no cavity wall insulation using 100mm thermalite blocks in the inner skin. This met the spec as it was back then. Chances are they would solve the cold bridging.

@deanmsimpson

Жыл бұрын

@@harveysmith100 Yes, very interesting. I prefer the idea of having the inner skin of the parapet wall being constructed from solid blocks as opposed to stud-work. Thank-you for your reply Harvey 👍

@londonengland7096

Жыл бұрын

I have a 40 year old extension built of 1 single therma block wall and cold roof that had that loose wool type insulation and no vapour barrier iI never once had any issues until now when I got it redone

"If you don't know what a parapet wall is, then why are you watching this video!?" Roger, you are a legend.

Good vid Rog but I wouldnt mind some photos of one you done earlier. Got to do some 1200mm high PP walls on my back extension if I get it started this year as a wind break for a first floor balcony. 😁

Great video. 👍🏽

You are the man.

Parapets can also be detailed as balloon-type timber frame to help reduce cold bridging. Keeps it rigid.

Thank Rog! That's a fantastic explanation of the issue. Why is it not built correctly in the first place to remove thermal bringing? Also why not run the membrane all the way over to be sure there won't be water ingress? Cover it with some nice trim coping cap that hides the membrane.

Very wise, worth a subscribe for sure. Thanks for sharing.

@SkillBuilder

2 жыл бұрын

Thanks for the sub David

Great, educational stuf to consider before getting to that point. Watched it twice

Architects love them. Important to get into the grove.

Excellent explanation Roger, I definitely prefer a roof with a good fall to shed the water and channel it away safely. Wish you were in business near me.

I agree-spot on as ever thank You :)

Spot on

Yes. The grubby, stained wall effect. Loathsome. In cold wet areas the bricks can get wet and overnight freezing gives a beautiful spalling effect.

Interesting that. Nice one 👌🏻👌🏻

Steve Roofer/London flat roofing is an absolute Jedi Master when it comes to flat roofing, top bloke too.

@SkillBuilder

2 жыл бұрын

We agree

Thank you for our content. I would use external insulation on the inner layer of the parapet, which will stop any cold bridging. This method works perfectly in countries where the winters are very cold, and the autumn is very humid. Your solution is very good, but it makes the detail too complicated.

There are new load bearing insulation blocks (like Marmox Thermoblock) that removes the thermal bridging and is rated up to 9Nm. Currently using it for an extension project below DPC and parapet.

@SkillBuilder

2 жыл бұрын

The 9nm block is not a great insulator. You could use a 2.8Nm on that inner skin above the roof line. Good point though

@Rob-tg7nr

2 жыл бұрын

came here to say this, not sure on their reply

@robinbennett5994

2 жыл бұрын

They also sell a heat resistant variety especially for parapet walls. The regular stuff can melt if the a bituminous membranes is applied with a flame gun.

@designcoordinationmanageme3177

2 жыл бұрын

The thermal co-efficient of aereated blockwork, whilst better than dense, is only about 1.1 vs 1.2 ... when you do the calc's, it alters the U value very little, and only insulation has any real effect. For comparison, insulation is generally 0.4 for the poor stuff, 0.2 for the good. Insulation only needs to be part way, if you do thermal model contouring it will show a point where extending the insulation after that point is of nil effect. Insulation is key.

@sonandmoon2958

9 ай бұрын

​@@designcoordinationmanageme3177 love, love love it, new your talking my language Padawan

Roger, I love parapet walls when they are built correctly. Especially when built on a rear extension as a party wall. It allows the neighbour to abut the wall at a later date at perhaps a different height from the first neighbour and without interfering with their roof covering. But they MUST be built correctly.

@SkillBuilder

2 жыл бұрын

Perfect party walls in roofs were a fire regulation and, as you say, done right, there is no problem

Great taught me something about the improved design but its always old parapet walls on OLD BUILDINGS

I think you are spot on - avoid parapet walls if you can. And double height splay bay windows too but that is a whole other story....

Great video. Does part explain a problem I and many are having with a open air Deck access & wall of is above our dwellings. Two years and the factor owned by Housing Association refuses to act and the Council, cannot even offer to inspect and declare below tolerable property. And not one RICS local Building Surveyor accept the job, either citing conflict of interest or they just don’t want the job. Sooner covid is a non news story the better.

Great video Roger!We have 2 parapet walls, nothing but hassle and complication!They came about years ago when the second owner put up a ground floor extension on the rear of the property and then decided to add another one next to it about 5years later.Really I would like to do away with them and make it a single roof instead of 2.Just don't know if I can handle all the upheaval involved.🤔I just wish people would think more before they do these things.

I had exactly that problem but persuaded the builder to replace the coping stones with lead, 40mm outer overhanging and approximately 300mm on the inside, with the grp tucked under. Two years ago, all dry and me and the missus very happy!

@SkillBuilder

2 жыл бұрын

Good idea you can also get zinc cappings.

Good video, seen loads of these roofs and always thought they looked good. Didn’t know about the issues with them though, again just comes down to that state of builders in the UK these days. Hard to find good ones now :(

great idea that makes scence

totally agree with you

I love your videos, great info on the good and the bad ie what to include and what not to include in a build. Super! Super! However, I am struggling... I'd like to know that if you were to build a new build whole house from scratch, which building method style /system/foundation would you prefer... brick or render, just sip or sip and brick, or wood frame etc.. What would you design your own house to be. Please help with videos to help me/others choose what to New Build... and where to begin, with future vids. Many thanks for your EXCELLENT Videos Roger!!

There is a really good video by stewart hicks on flat roofs that goes into quite a lot of detail. The problem here doesnt seem so much exclusive to parapet walls as a conflict of older and newer construction where insulation and air tight design mixed with older methods often leads to problems like condensation, mold, siphoning and trapped water in the event of leaks.

good opinion

That’s a great idea I’ve come across issues my self with parapet walls but we would fit air vents to get rid of any moisture and wrap the roof membrane over to the outside skin glue the coping stone and silicone seal the joints not mortor

Makes sense👍👍

Nice one Roger. The height of the parapet can also create problems for the structure due to wind and snow drift loadings. If its too high you may need to add buttressing to give the wall some lateral stability. As you say, better with an overhang.

@jamieshirey4926

Жыл бұрын

From the pictures I've seen recently most houses there don't have walls either lol

Amazing❤❤❤

“If you don’t know what it is, why are you watching?” That’s an easy question. I figured you wouldn’t talk about archers and medieval architecture - or WWI trench construction. So I was curious to learn a bit about it! Thanks for your description and construction alternatives.

I have an extension on a bungalow being built, planning insisted on a parapet wall, they objected to a pitched roof to match the rest of the bungalow as it would impact on the light linked to the neighbouring semi detached house.

Brilliant video mate! Love the studwork idea rather than turning the internal blockwork into external above the roof. I've did a small parapet wall Friday. However the way it was set out allowed there to be no cold spot.(I think) Overall the wall was 410mm. Face Brickwork tiny finger gap then blockwork then 100m cavity and internal blockwork. Once above the roof line, I returned my Brickwork onto the finger gap blockwork, as in theory that is still an external wall🤔👌 Worked well, but at alot of extra cost. Great video as alway mate

@SkillBuilder

2 жыл бұрын

That sounds like a really good way of doint it

Even am almost 80 I just can't stop watching your videos mate maybe knowledge is valuable at any age, one think I always wanted to do was install an air to air heat exchanger, even I got one free from a job I was doing the mere mentioned of that started my EX n that was enough how I wish I left her ages ago thanks for your videos mate