A Deeper Dive Behind Parapet Walls
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- เผยแพร่เมื่อ 19 พ.ย. 2024
- Roger digs deeper into the pros and cons of parapet walls.
Check out Parapet Walls 1 🎬 • Parapet Walls - Are Th...
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#ParapetWalls #FlatRoof #Parapet
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I had no issues understanding the first video but nice that you reiterated it.
I live in the American Northeast in a neighborhood of 19th century brick townhouses [parapets are a common feature] and where we go from below freezing winters to steaming humid summers [-15c to 35c] and folks have spent the last few decades stuffing up insulation and sealing cracks and these 'damp lines' are rampant.
Excellent graphics there Skillbuilder, these types of drawings make more sense for people to understand, and Roger can throw his pens away.👏👏👏
It might seem odd but you must remember heat loss can be material (like a steel wall tie) or geometric - in the case of a parapet the upstand acts like a cooling fin. The heat-emitting surface is larger than the heat-absorbing surface, just like any other corner. Hence why the heat break is important!
Fantastic explanation! Thanks Swwils!
Thanks for explaining this! I've had this problem numerous times over the years and now that I think of it, yeah...always at the chimney or bellow a parapet.
The comment about condensation on a cold chimney breast is spot on exactly what happened in my mother’s old house….She had a repair chap rambling on about flashing and sealing etc, but you could see the ceiling water stain coincided with a change in chimney profile in the loft. Condensation was running down the outside of the rendered chimney brickwork in the loft and dripping off at the curve to wet the ceiling board under it. I guess it only occurred on cool summer nights when the fire was not lit. This is hard to fix, but one way is to install a collection trough under the drip zone and pipe the run off to an outside wall or under the eves harmlessly discharging the condensation.
One thing I’d add is, take the membrane down the exterior wall a little bit, and ensure the cope is only there for decorative purposes .
Good point
the membrane under the coping SHOULD show a half inch , i know it looks ugly but it WORKS !!
@@pauldavies5655 - where is the attachment of the coping ? With the membrane right under the coping, you may be risking detachment in high winds.
@@thetessellater9163
you can do it easily with DPC --- it will take a wind of over 120 miles an hour to dislodge a coping done properly.
i know of coping stones in britain at the end of 4 storey roofs ( we call em FINIANS ) which have survived a 120 years untill the main roof covering needed changing !
also look at the shape of each coping stone and adjust it to the wind conditions in that area --- common sense !
remember , make it secure -- make it WORK , NOT make it look pretty !
I had a bit of a giggle watching this, because, like a typical builder, at approximately 0.20, Roger says "this is a very quick video, won't take two minutes of your time."
The video then continues for another five minutes and eleven seconds!
That means this video lasted 16.6 times longer than he said it was going to.
It's a good job he wasn't quoting time for a new installation!
Only kidding, Roger.
I love to see your videos, they are brilliant.
I knew when I said that it would be hard to get it in under 2 minutes. I should have shut up.
"This kitchen and flooring reno should only take a couple of weeks...", said I to my client a month ago 😂. Might be done end of next week.
Another great video as always Roger. We've got a 1st-floor balcony with parapet wall with capping stones which has rotten timbers (firrings and joists) around the perimeter under the OSB deck, especially under the internal corners.
You and your diagrams explain well "how it should have been done at the beginning". But that doesn't really help me in my pre-existing situation. Perhaps you could make a video about how to fix this system without the demolishing and rebuilding of the entire parapet. Roger that!
Please more of these type of videos Roger,
Underneath the GRP they should use slate or cement board rather than OSB/chipboard wood which in time will absorb moisture. Great video Roger
No OSB 3 is great. A lot of GRP suppliers insist on it.
Hi Roger, great video as always. I actually thought your original video on this very straightforward to understand. Was just after a detail on venting a flat roof with a parapet if you had any?
Thanks Luke
Another great video - thank you. What kind of insulation would you use to run through to connect to the wall insulation? I mean in terms of building block work on top of it - does it have to be anything special to support the block?
I'd love a video about how to properly do a chimney and the different types to prevent what you mention. In my property I was thinking about just pushing some insulation in to is to try and get it above the ceiling line then caping the top to prevent any rain getting in.
The best solution is to simply use a wider coping stone and extend the inner leaf's vertical insulation (25mm thick) all the way upto the coping stone. Plus use thermolite on the inner leaf. =strength and no cold bridging.
Should there be some form of vent at the top of the brickwork to allow flow of air and allow any moisture to evaporate??
Most modern weep vents also allow some cavity ventilation. They also can prevent pressure differentials so moisture is not forced into the cavity.
Nice thermal bridge down the block work inner skin to the roof slab! You also need a separating membrane between the vapour control layer and the slab/blockwork to minimise the danger of perforation during the construction process. On the whole, using an inverted roof is infinitely more preferable not least because it avoids thermal stress to the edges of the main water resisting membrane and early degradation from its direct environmental exposure illustrated here.
Nice one Rog 😁👍🏼🧱
Hi Roger.
I would happy to send you my standard detail for parapets which does address the issues you have been highlighting.
Your videos are very informative, I’m always referring to them when discussing details with builders
Regards
Richard
Hi Richard
Yes please it would be good to see. We have a couple of variations from viewers so it would be great to see them side by side.
That would be great to see. Perhaps Roger could show them in another video? I'm always keen to learn new insulating and flashing details, even if my work here in Canada is much simpler. Cheers!
@@SkillBuilder not sure I can upload PDF images on here would it be best to email you?
@@richardphillips7581 Can you email to me please?
@@brianstorm4806 yes but can’t seem to find your email address
Possible to just have the outer skin of brickwork as the parapet and to finish the innner skin of blockwork just below the roof deck, taking the deck and the warm roof insulation right over to the brickwork, thus closing the insulated envelope right across. My fave waterproof membrane is GRP - you end up with just one piece for the entire roof covering
The only problem is that the 4 inch brick wall is not that stable.
Great thank you made alot of sense however could you explain where you would take the vapour barrier
The principal is to stop airborne moisture getting into the roof so the vapour barrier needs to lap up the side of the roof to the top edge.
@Skill Builder how can it if you have the top deck on top of the insulation and then build a stud wall on top deck if the insulation is going right though to stop the coldthen how do I get the vapour barrier back up the outside wall do you screw the stud wall on top of the vapour barrier?
Bit confused sorry
What about the first layer of bricks on the inside wall, on the concrete deck being foamglass bricks?
Hi Roger .. I have been having a "nightmare" for the past year regarding a parapet wall and flat roof .... However .the difference is its a house built in 1885 with no cavity walls .! .. I've had about 8 different roofers, none of whome can offer a solution ... except to try to rip me off ! ... There is celotex between the joists pressed up flush with the boards ...... I made a hole in the bedroom ceiling beneath and removed some of the celotex the underside of the board is soaked ! .... could this be osmosis from where the condensation is created in the parapet wall and soaking into the edge of the boards which vgo right up to the walls ?? I am in total despair ! And have had a lovely flat sitting empty for a year !! .please can you help or advise .Rick .
Great vid. No osb in England on roofs. Use only plywood pls.
You are wrong. OSB is specified over ply because ply delaminates.
I hate Osb. Yuk.
Part 3 to include concealed gutters (emailed detail)? Excellent video!
Coming soon!
Good explanation (and better illustration) of the design issue. Could you do one on commissioning an external brick chimney. We have decided to decommission ours and insulate our North wall (internally) and I am wondering about the long term health of the interior of the chimney re condensation/ventilation/ capping/.??🤔
I had that problem with the chimney, had it reflashed, repointed and a capped off with a tin cap. what a waste of time it still had problems so it was taken down top to bottom (removed) and how much warmer the room is now. please do a video on this to show how bad chimeys are for heat loss ( its like having a window always open).
Good idea
Could be useful for 'trickle venting' the house though. Chimney breasts are also used for lateral restraint on a long wall, if you and your neighbours both remove them, there could be issues with stability.
Great info what can be done about it?
Where can you buy the pre formed‘saddle style’ parapet on your illustration please?
It's not always a leak, quite often just a damp stack of chimney.
I have a real issue trying to detail warm roof, with balcony deck above with frameless glass balustrade. Had originally thought a cast ring beam sitting atop inner leaf would be substantial enough for balustrade channel to fix to, but SE is having kittens saying that a huge steel UB, bolted to roof joists, with PFC welded on top is the only thing that is 'probable on paper'. I think this is way overkill but will consider building a stub of parapet wall to decrease the glazed area, the tips here on bridging issues are good. BUT, I still need to have something 'suitably robust' to fix the balustrade to that doesn't pierce EPDM. For sake of argument lets say stub wall is 350mm from FFL, which leaves 750mm of glass. Answers on a postcard....
I have a building almost identical to the diagram. Except I have solid block walls with a cast concrete roof with steel RSJs going right through the wall.
It's an ex industrial building, I'd like to leave the ceiling exposed.
Can this be done and how? I'm getting many conflicting opinions
Thanks
Have you seen anyone doing the timber stud work on top of the insulation? I’ve got an upcoming extension with a parapet wall, I’m interested to know if this is a good method
Upstand studs are quite well performing insulator. You don't put insulation below studs. You put it between. If you make timber upstand it is way better than any concrete block or brick. Thermalite block is a different storry. Actually would be easy to find u values for timber and thermalite to compare. But premise of video with assumption of timber ceilimg would be that where timber beams rest on the internal wall, the wall continues with insulation layer, not block. Then you have a plate on top of insulation, dwarf studs on top of plate, then another plate just below caping...
Ceiling noggings 1- 3 inches away from wall. Osb board from top acting like a shield + noggings just next to the wall along with the dwarf wall bottom plate should prevent any warping on 4 inch support area of timber warm roof joists.
Previous video postulated moving temperature stress point (sorry not an engineer - point where cold crawling through material from top meets warm temperature crawling from the living space from the bottom) be moved from inside the living space somehwere inside the wall under the ceiling to somewhere inside fhe ceiling level, _inside the bearing part of the roof joists_.
I would guess that with an extra bit of the insulation marked on the above video as upstand, this temperature would move into the level of actual paraphet wall's upstand's timber plate (not marked on this video) and be as negligible as possible, but hey, Roger is a God of 'Why won't we consider *thiz* today' and i am sure there are dozens of people who would be inspired to get some science done and tell us how those things work.
Building is art and forgotten lore. Art is chaos. Forgotten lore is forgotten. We all have passion and try for the best but we are still shaken by paradigm shift that took place somewhere in the second half of XX century. We just try for the best.
@@kerel995 if you just have the stud work on top of the block work you’ll probably be better off going with thermolite block instead.
It would be nice to see some numbers/evidence
@@mooney0086 previous Roger's video said:
Insulation inside warm roof goes over concrete wall that ends at the bottom of roof joists. Then in between bearing part of joists you have full insulation. Upstand is on top of roof joists.
Regarding numbers, this is like a little nerdy math excercise
I would love to read calculations for timber bridging too ;)
@@kerel995 I’d imagine building control would want SE calculations for adding coping stones on to a timber frame too. More expense 🤦🏻
@@mooney0086 absolutely crossed my mind.
I like the way your brainz work ;)
Thank you : )
Any chance of a small model of it, I often find it hard to follow the lines, they are all really small, cheers
Sealing houses up is going to cause a lot of trouble in the future, not just for buildings but for people’s health. Older buildings were designed to breathe, they also had good regulated temperature - if they were built “correctly” of course.
That brick is structural. It isn't a veneer.
On the roof side, you could simply use any sort of framing. I recommend not using masonry on that roof side as it is just added weight for no reason.
Also, the outside brick would be preferable to be a veneer on wood or metal stud framing. Keep in mind to use proper sheathing and water/vapor proofing.
I want to cover my coping stones over what can I use on a budget.
I want to build a 12ft pier in blockwork how can you help,Thanks I enjoy your show
Would using multifoil as the insulation around the parapet wall upstand work to help reduce the thermal bridging?
Be interesting to look at the similar issue with gable walls in the loft, which must also eradicate heat out of the house above the insulation? Hipped roofs must lead to a more efficient building?
The inner leaf of the gable is not exposed to the elements, so warmer, but still must lose some heat to the outside. Maybe not enough cold bridging to form condensation, and if so, the ventilation in the loft should take care of it.
@@thetessellater9163 silly question, would the orientation of the building not affect the inner leaf of a gable? I.e, driving wind/rain?
Our gable is north facing, so it’s a cold wall anyway, but my point really was the temperature in the loft is very low above the insulation, and the inner leaf of the gable bypasses the insulation, so it must soak heat out of the house. Wasn’t particularly suggesting a condensation issue, just bridging.
Insulation is meant to be carried up at least 200mm up the cavity in the gable. The roof is also meant to have perimeter insulation - this is often missed on cold roof constructions where there will be a gap where no insulation is between the gable and the first ceiling joist before the horizontal insulation of the attic, usually exposing the room belows ceiling plasterboard corner to cold attic air.
Nice drawing. Is it Corel Draw?
Nice diagram taken from NHBC standards.
Random question - I'm fitting a kitchen and have taken the supply pipe work back to the rising main/ stopcock as it was so poorly fitted. it's a detached property. Combi boiler, no storage tanks and no outside tap. It does have mono bloc kitchen tap and a shower head on a hose over a bath. Does it require a double non return valve at the rising main? If it does is that best practice or legislation? Sorry asked a few people and got different advice :(
I don't know jack about plumbing, I'm only thumbing up your post in the hopes that someone else with knowledge might notice it and give u sound advice. Best of luck
Edit. Have you jumped onto an online plumbing forum?
Marmox thermoblock will aleviate the cold bridge
Look forward to the live build show…… I work in construction but about to start my own new/extension/refurb build….
Not the first one I’ve done but need to up my skills and knowledge
... "need to up my skills and knowledge"... Don't we all my friend! Me too!!!
Can Marmox Thermobloc be used at the warm roof/inner wall leaf junction on a parapet?
I was just thinking the same thing. It doesn't seem to be very well known about as a product, the jury's out in that one, but it would be nice to hear from someone who's actually used it.
Why are building standards not reflecting this? Why are blocks still used if studwork is the ideal solution? Also, would termalite blocks solve the problem?
Alao, would insulating the inside edge of the warm roof solve it? There’s plenty of space between the rafters…
Thank you so much Sir, for volitionally imparting construction knowledge....
"My drawing is absolute rubbish" hahahahahahaha
Nice
Would you have the same problem if the roof was timber, joists and plywood top, with insulation in-between joists
That would be a 'cold roof' which is less efficient.
Hi I watch you program on you tube and I value your knowledge , my new neighbours are doing a loft conversion and the party wall agreement has been done but does this include work on ground level as I have just found out that they want to build a wall next to my fence in which will take my fence down and start building in which it will possibly block out the light can you let me know what think , thank you for your program ,
Regards Pat Flynn
The Party Wall agreement should cover all aspects of the groundwork too. There is no 'right to light' as some people assume. They should have no right to even put foundations on your land, so make sure this is stipulated. You can use your own Party Wall Surveyor, to look after your interests, for which your neighbours must meet the cost of.
What about lead parapets?.
Where is the lead?.
This video clarified things more.
But could you not leave the inner brickwork away altogether above roof level and use a rigid form of insulation (PIR) above roof level?
The roof membrane does keep water out of your wall cavity anyway in this scenario.
You would only end up with a somewhat narrower coping and just the outer wall to fix you coping to, but in the case of aluminium or zinc which is relatively light this must be not a problem.
Or are there things I don't see?
I was thinking that but I think as it’s a cavity wall you still need to tie the top part of the outer brick skin to the inner skin, and I assume you can’t fix steel wall ties to PIR
@@charlespudge3371 I think that when the parapet wall isn't any higher than a foot the single outer leaf can do well without the ties, but when you have a 4ft high parapet wall to act as a barrier around a roof terrace this is a different matter.
In my case I'm looking to build parapet walls which are more like upstands for the roof but with a metal coping over it to look like a proper parapet wall from the outside without having barge boards or such.
Dew point
I don't agree with building the parapit on top of the insulation
No mechanical fixing so would slip/move about surely? Or is that just me
Thd cavity may have to maintane its m value so dont think your desire to use insulation would work .
I have never layed a block on screed in my opinion the drawing is wrong ...where is it from Rodger...?(Brickie 33yrs exp)
@@stuartnicklin4101 seen the diagram in the nhbc standards - flat roofing
😱😱😱 we need to turn the sun 🌞 up a few degrees, like they were promising 40 years ago 🤭
Your grandchildren will be saying the opposite as they try to deal with global warming !!
@@thetessellater9163 maybe! maybe not! Heard of the cooling cycle, we're heading for another ice age. Anyway l,d be more worried about stray asteroids coming from deep space, on the bright side we're won't know what hut us. 🤯👍🎯
@@MikeAG333 🤔🤣🤣🤣
For people that actually know what they are doing, I found Roger's white board sketch better. This diagram has issues, which Roger pointed out. But again, I understand such issues because I deal with such issues, and not everyone does. One's audience can vary, and some may need the least common denominator, especially on TH-cam. But not everyone. So, and after that being said, Roger --- do not throw away your pen and white board. Some of us do actually "get it"..... 🙂
Thank you, I just need to calm down and learn how to draw
I preferred the original diagram 😂
Nothing wrong with the original video in my opinion.
i am a roofer from wales -- for over 30 years .
i bloody HATE parapet walls because when and if they go wrong it is ALLWAYS the roofers fault --- not the surveyor , the architect nor the planner but the roofer !
and none of those f..ckers listen to us !
( i wish they would )
I am with you on that Paul.
@@MikeAG333 - my 'architect' submitted my plans to Building Control and had 17 revisions to make - not all architects are equally knowledgeable - he learnt from me too over the need for a short section of corridor for fire regs.
@@MikeAG333you may listen but it s a shame other architects do NOT !!
we are at ground ZERO all the time , you boys sit in offices a lot of the time -- work it out mate !
ps -- and yes planners DO have an input because they allways want things to look pretty NOT how they perform in conditions they know very little of !
@@MikeAG333 well i actually AGRRE with you on that ,BC and town planners are in bloody world of their own sometimes.
they do not ever take the blame if their conditions are a LOAD OF SHITE !! lol
they just work for the government in most case s and their job is protected anyway ! it is the builders name which becomes mud due to very poor plans and conditions we are subjected to .
@@MikeAG333 lol, well there you are then as i have worked for "english heriitage" " the national trust" CADW , the army and the government .
they all have listed buildings !
PS--- if any council has a certain VISAGE for the area due to a councilors preference then it will be followed through regardless of any architect or builder my friend !
👋👌👍✅
D D D Did You See The Frightened Ones?
That's better. The drawings I mean. However, there is still cold bridging to raising the full parapet wall above the roof with all the added risks of exposing a cavity wall and then relying on an out of date concrete coping. Just extend the outer skin only above the roof and use a proprietary powder coated aluminium capping system with hidden fixings over the single ply roofing membrane. That way the warm deck roof oversails the inner skin and cavity. Your detail is so out of date. Any parapet wall roof abutment is like going out in the rain only wearing a fez hat rather than a hat with a decent brim. Your ruddy ears are going to get soaked. AVOID parapets at all costs is my advice.
Uk is really moist.