Hopefully this video will help explain the difference between a warm flat roof construction and a cold flat roof construction. This video shows detailed drawings on how a warm flat roof is constructed. I link to two other videos, one on cold flat roof construction and one that’s an in depth comparison between cold and warm flat roofs, also showing thermal imaging of poorly performing, insulated flat roofs. The animation program I used was Sketch Up with lots of section cuts.
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Having watched many of your excellent videos, I decided on a cold roof because of thermal bridging issues. I must disagree with a comment made at the end of this video based on theoretical knowledge only i.e. no access to thermal imaging equipment. The joist hangers would still be a source of thermal bridging on a warm roof because the wall they are attached to is an external one. As hot goes to cold, the room heat would travel into the plasterboard, then the joists, then the joist hangers and then to the brick and then out to atmosphere. The house extension I have constructed has 150mm of XPS insulation in between the joists, 50mm of EPS insulation underneath the joists, an unvented 50mm air gap and then the plasterboard. There is also no thermal bridging from the block walls as they are all covered with 50mm EPS bonded to the wall and then bonded to the plasterboard with PU adhesive. In my opinion, this is about the only way you can cut thermal bridging to its minimum value with todays construction methods. Just as a FYI, I chose XPS because its LTTR (Long Term Thermal Resistance) figures remain [...]
Constructing a warm roof on a new extension with parapet walls, I will have surplus amounts of insulation left over and am considering adding this insulation to the underside between the joists to double up the insulation, would this install have any negatives?
Unless Europe has some miracle EPDM I don’t know about after 4 decades as a journeyman roofer the walls ,roof curb and chimney flashing will all fail within a decade ,the rubber will shrink and pull off the walls ,a product that Firestone ,Versico aka Goodyear and Carlisle EPDM roofs mandate at walls is called RUSS strip amd you didn’t install it ,RUSS is a 6 inch wide 60 mil roll of heavily reinforced EPDM that sits flush at the break in the walls & deck ,it gets screwed and plated every 8 inches ,then your field sheet of rubber is glued directly to the RUSS stripping before being rolled up the wall as flashing ,RUSS completely eleminates the natural shrinkage of the field sheets from pulling the rubber off the walls ,in USA RUSS is also used around all penatrations such as soil pipes and such , why no RUSS strip ?
Hi Steve As discussed on the phone we are looking to have our flat roof (extension at the back of the house) insulated and the roof covering replaced, as the current and we’ve had a leak into our son’s bedroom below – probably where the drain enters the roof. A builder said the roof covering should be below the black bit around the bottom of the drain, not above. The roof is roughly 2.25m x 6.35m. I’ve just realised that it will be dark by the time I get home tonight, so I’ll take pictures tomorrow morning. We have been considering high-performance mineral felt or EPDM as a roof covering. What would you suggest? As I said I looked at the Energy Saving Trust website which says a flat roof should preferably be insulated from above, by installing a layer of rigid insulation board on top of the timber roof surface with a new weatherproof layer on top of the insulation. many thanks best wishes
Hi, Steve, Cold bridging is shown on a ceiling. The metal will not get “colder”… It can only get as “cold” as the ambient temperature it is “contact” with…Sorry, about the three replies, but I wanted to address each point separately…That I beam, is at the top of the roof, near an exterior wall, with no “top load” (of significance) and appears to be acting like a ledger, for the roof rafters and ceiling loads…But, it also appears to not, be supporting the ceiling below…(appears to be a gap between rafters and ceiling. Either way, the point is, keep the barrier, on the heated side of the “insulation” or you will be putting your dew point in the insulation in the this “detail”…Oddly, the “heated side”, could, in fact, be the roof side and NOT in the inside of the house…depending on temperatures of your drawing’s location (in the world and daily mean temperatures)…Also, more consideration should be given to venting all roofs.
EPDM rubber flat roof with two new skylights High-performance mineral felt? EPDM Rubber? Reinforced liquid roofing system? As a company, we don’t use a naked flame on a roof, so we don’t use felt. No flames no fires. If we did I we still wouldn’t use mineral felt, felt only comes 1m wide, so you end up with lots of joints, joint means possible leakage at some time We use EPDM rubber, its good and comes in large sheets, fewer joints fewer problems down the line. We use reinforced liquid roofing systems because there are no joints and it’s easy to do detail. (We don’t do glass fibre (GRP) to brittle) This is a liquid roofing system and is good for doing details. So you ask how do we choose between EPDM rubber and a reinforced liquid roofing system? We let the roof chouse if the roof is mostly open and doesn’t have much in the way of details its EPDM rubber all day long. If it’s covered with detail like pipes pocking though it, or airconditioning units and skylights all over it, then its got to be a liquid system.
Its that time of year when condensation inside your roof will start to form, the lack of ventilation, insulation and movement of warm moist air from inside the building can all be part of the equation. Have you ever wondered where the moister on a cold bottle of wine or a bear from the fridge comes from? Its the moister in the air condensing on the side. When the containers warm up, this stops happening. Not no good if you want a cold drink, imagine having a magical dring container that keeps itself cold forever fantastic however the condensation will drip off the bottom and make a puddle as long as the relative humidity is high. Now think about your roof, outside is cold ( like the container) Inside has heated air, that can hold moister. If your insulation or ventilation between the internal and external parts of your roof is not correct, water can condense and drip down onto your ceiling. Not good, attention to detail, when installing new roofs flat or pitched, is paramount now that we heat our housed and insulate to the today’s standards.
New Flat roof Harrow. This is a cold flat roof as its has vent on it This new felt flat roof is about five years old; venting has been added to the roof as it’s a cold roof however it was found that the roofers put the new flat roof insulation on the top and formed a warm flat roof. Unfortunately, this roof is now not warm or cold but a highbred roof, and it’s not performing correctly.
Supplier, best vapour barrier for flat roofs on the market. There are four suppliers that I know off that will supply this self-adhesive best vapour barrier for flat roofs. Only one of them will supply by the meter, and that is: www.rubber4roofs.co.uk If you use our promo code LFR2013, you will get our discount (if the promo code is not working phone and mention this site and get the new one) Why is it the best vapour barrier for flat roof? Vapour resistance of 2000 MNs/g Self-healing if punctured by fixings Temporarily waterproofs the roof ( can stay uncovered for up to 3 months) Self-adhesive Easy to install Its not cheap, purchasing it by the role and by the pallet load is cheaper but is a considerable layout. This video shows me testing the vapour barrier when we did a job late last year. A primer for the vapour barrier is recommended if you are going to glue down over the top of a surface that not sound and should also be used if its cold. It sticks very well sometimes too well if you let it touch itself you have to throw it away as you just won’t get it apart. If you are going to order this for a flat roof and [...]