Parapet Walls — Are They A Good Idea?

Roger looks at the pros and cons of parapet walls.

Check out the Steve Roofer channel and London Flat Roofing.

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#ParapetWalls #FlatRoof #Roofing

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[JamesBrown-mtru]

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.

[franklinkarrass]

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. 👍👍

[American-In-Mykolaiv]

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!

[Tensquaremetreworkshop]

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.

[spyrosspyrou]

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!

[lambjf]

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.

[kelstra]

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.

[effervescence]

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.

[JohnnyMotel]

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.

[kevinrae]

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.

[harveysmith]

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.

[randomtask]

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.

[bwild]

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.

[SuperVitz]

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.

[JadeBoily-co]

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.

[YipeeKiYayJB]

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.

[AltaMirage]

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.

[mattylad]

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.

[macitect]

As an architect, I wondered at first where you were going with this, because I have always detailed it as you advise - either single skin at the top, or with metal/timber stud construction. The only thing I don't agree with is that it is a trend that will go away... When detailed and built properly they work fine, and we have plenty of precedents like the Georgian buildings of Bath with the set back mansard roofs. I think parapets are here to stay. Anyway, fantastic video, I've been a long time admirer but I don't normally comment. Thank you!

[NitrousAvster]

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.