WWilts Posted October 13, 2021 Share Posted October 13, 2021 (edited) Brick and block. 110mm cavity to be insulated with bonded blown EPS beads. For penetrations (eg extractor fans) what is the sequence of installation? Blown beads last? How is the thermal bridge reduced, if at all, when there is such a huge penetration through the insulation? Context: limited budget. Keen but not desperate about thermal efficiency Edited October 13, 2021 by WWilts Link to comment Share on other sites More sharing options...
Moonshine Posted October 13, 2021 Share Posted October 13, 2021 (edited) i would build the walls with the cavity, core drill out 100mm hole and put the 100mm round duct through and seal the perimeters of the duct, before plastering and ceilings. Thenfill with EPS beads As for thermal you have a 100mm hole in the wall and the only real way i know to reduce the cold issue is with shutters, though would be interested if there is a better way. Edit: if there is a duct run in a ceiling void you could wrap it with insulation Edited October 13, 2021 by Moonshine 1 Link to comment Share on other sites More sharing options...
TonyT Posted October 13, 2021 Share Posted October 13, 2021 Plastic sleeve in the hole? 1 Link to comment Share on other sites More sharing options...
WWilts Posted October 13, 2021 Author Share Posted October 13, 2021 38 minutes ago, Moonshine said: shutters, though would be interested if there is a better way did a bit of research. Perhaps a spring-loaded backdraft damper would improve slightly on shutters. There must be UK versions of this US product https://www.homedepot.com/p/VENTS-US-6-in-Galvanized-Back-Draft-Damper-with-Rubber-Seal-KOM-150-U/205715170 Link to comment Share on other sites More sharing options...
Ferdinand Posted October 13, 2021 Share Posted October 13, 2021 Spring loaded backdraft damper is one way. Or get a fan with a built-in backdraft shutter. There are plenty around. If you want something sexy looking there are the Airflow Icon range. Or better get a through the wall HR recovery fan. I have been using Lo Carbon Tempras from Vent-Axia for 7 or 8 years, as they have a trickle setting. I use them in conjunction with a PIV loft fan, which gives me a poor-man's MVHR to protect my houses from interior-wash-drying tenants. Not exactly sure how you would do this once the beads are installed, but see para below. Though I'd enjoy a video of all the beads from your entire house gradually filling your kitchen, if you can get one ?. My standard method of install is to insert a section of 102mm soil pipe in the wall using foam at a shallow angle down towards the exterior (for drainage of any moisture) sticking out a little on the outside to keep drips off the wall, and mount the fan in that - perhaps just tacked in with foam. That makes replacement easy and works well with a HR fan with the heat exchanger in the hole. I think the way to do after-beads would be to core drill through, then push it out from the other side with your piece of soil pipe. Ferdinand 1 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 13, 2021 Share Posted October 13, 2021 to meet current NHBC regs it needs a tray above it. 1 Link to comment Share on other sites More sharing options...
TonyT Posted October 13, 2021 Share Posted October 13, 2021 NHBC regs? I thought building standards wrote the regs? 1 Link to comment Share on other sites More sharing options...
Ferdinand Posted October 13, 2021 Share Posted October 13, 2021 10 minutes ago, Dave Jones said: to meet current NHBC regs it needs a tray above it. Chapter and verse would be good. (I note that the OP did not ask for a full comment - just how to do the penetration) 1 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 13, 2021 Share Posted October 13, 2021 2 minutes ago, Ferdinand said: Chapter and verse would be good. no problem. https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/6.1/ducts-flues-through-core-drilled-holes-.pdf 2 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 13, 2021 Share Posted October 13, 2021 11 minutes ago, TonyT said: NHBC regs? I thought building standards wrote the regs? they do, warranty providers though are more demanding..... Link to comment Share on other sites More sharing options...
Ferdinand Posted October 13, 2021 Share Posted October 13, 2021 2 minutes ago, Dave Jones said: no problem. https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/6.1/ducts-flues-through-core-drilled-holes-.pdf Thanks. I see that the cavity tray over only applies to Newbuild, but not retrofit - which helps clarify depending on the OP situation. Quote Answer Where a duct to an extract fan is built-in as the wall is constructed it should be provided with a cavity tray to protect the duct from mortar droppings, which could bridge the cavity and cause dampness. Where a duct to an extract fan or boiler flue is installed through a core-drilled hole after completion of the wall it is not essential to provide a cavity tray although the provision of a tray during the construction of the wall is considered good practice. Link to comment Share on other sites More sharing options...
Mr Punter Posted October 13, 2021 Share Posted October 13, 2021 2 minutes ago, Dave Jones said: no problem. https://www.nhbc.co.uk/binaries/content/assets/nhbc/tech-zone/nhbc-standards/tech-guidance/6.1/ducts-flues-through-core-drilled-holes-.pdf The point there was if you install the duct before the wall is complete it may gather mortar droppings. In reality the hole is drilled after and the link says is is not essential "Where a duct to an extract fan or boiler flue is installed through a core-drilled hole after completion of the wall it is not essential to provide a cavity tray although the provision of a tray during the construction of the wall is considered good practice." 1 Link to comment Share on other sites More sharing options...
Iceverge Posted October 13, 2021 Share Posted October 13, 2021 Been there got the t-shirt. I did it the most awkward way possible. 215mm inner leaf 250mm cavity 100mm outer. Waited until the wall was insulated with beads. Drilled a center hole and then stitch drilled a 150mm hole. Chiseled out the concrete blocks . Watched a large bucketful of "bonded" EPS beads fall out on the floor. Used a water drum to float seperate them from the concrete and rigged a vacuum cleaner in reverse to inject them into the wall again. Slotted through my 150mm pvc duct. Used a long nozzle of low expansion foam to fill the rest of the gaps in the cavity. Sealed the hole with a sand cement mortar. Cut off the pipe flush outside. Painted the duct to the blockwork 2-3 times with airtight paint both inside and out. Installed a double door magnetic anti backdraft damper in line with the middle of the insulation. All I needed to do was install a good recirculation fan or get the bricky to build in the duct first time round. As for cavity trays made from dpc membrane. A personal hate of mine. If I had my way again I would use a 120deg pvc profile built into the outer leaf only over penetrations. If the water reaches the internal leaf you're goosed anyway. 2 Link to comment Share on other sites More sharing options...
Ferdinand Posted October 13, 2021 Share Posted October 13, 2021 A long 102mm holesaw can be a useful investment. Or ask a fitter (eg gas or drainage) who has got one to drill your hole when he has half an hour at the end of the day. 1 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 13, 2021 Share Posted October 13, 2021 59 minutes ago, Mr Punter said: The point there was if you install the duct before the wall is complete it may gather mortar droppings. In reality the hole is drilled after and the link says is is not essential "Where a duct to an extract fan or boiler flue is installed through a core-drilled hole after completion of the wall it is not essential to provide a cavity tray although the provision of a tray during the construction of the wall is considered good practice." although the provision of a tray during the construction of the wall is considered good practice. The guidance is there for a purpose at the end of the day. To protect the building. Link to comment Share on other sites More sharing options...
Mr Punter Posted October 13, 2021 Share Posted October 13, 2021 7 minutes ago, Dave Jones said: The guidance is there for a purpose at the end of the day. To protect the building. I never see them being built in as the build progresses and never see a tray put in above. The chances are the sparky or plumber will locate the duct or flue elsewhere in any case and they will not be dimensioned up on the construction elevation drawings, so no chance a tray will ever appear in the right place. 1 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 13, 2021 Share Posted October 13, 2021 1 minute ago, Mr Punter said: I never see them being built in as the build progresses and never see a tray put in above. The chances are the sparky or plumber will locate the duct or flue elsewhere in any case and they will not be dimensioned up on the construction elevation drawings, so no chance a tray will ever appear in the right place. i agree. Just takes a little thought though. wherever the flue is going o be placed put a 2m tray above to give leeway. It can only help cant it ? Link to comment Share on other sites More sharing options...
Iceverge Posted October 13, 2021 Share Posted October 13, 2021 If you install a plastic duct with a downward slope what are the odds of any water making its way to the inner leaf that a cavity tray would solve. 2 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 14, 2021 Share Posted October 14, 2021 10 hours ago, Iceverge said: If you install a plastic duct with a downward slope what are the odds of any water making its way to the inner leaf that a cavity tray would solve. because it costs pennies to do and can save thousands. You could use the same argument for roof tyvec under the tiles, why bother if the tiles are providing the protection ? 1 Link to comment Share on other sites More sharing options...
markc Posted October 14, 2021 Share Posted October 14, 2021 11 hours ago, Iceverge said: If you install a plastic duct with a downward slope what are the odds of any water making its way to the inner leaf that a cavity tray would solve. In an ideal world you could put in a cavity tray, but where? Ducts/flues are often within a couple of inches of the ceiling or soffit so the cavity tray would go directly under the joists? That’s not good. A full course of blocks down would probably be too low so you end up splitting coursing. I’ll stick to boring the hole afterwards and sleeping it. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted October 14, 2021 Share Posted October 14, 2021 (edited) 2 hours ago, Dave Jones said: because it costs pennies to do and can save thousands. You could use the same argument for roof tyvec under the tiles, why bother if the tiles are providing the protection ? Can you explain how water will track in along a downward sloping plastic duct and won't along a cavity tray? A cavity tray has the potential to prevent proper insulation around the duct (with blown in insulation) leading to condensation. A cavity tray has a much higher chance of catching mortar droppings bridging the cavity completely. Edited October 14, 2021 by Iceverge 2 Link to comment Share on other sites More sharing options...
Dave Jones Posted October 14, 2021 Share Posted October 14, 2021 2 hours ago, Iceverge said: Can you explain how water will track in along a downward sloping plastic duct and won't along a cavity tray? A cavity tray has the potential to prevent proper insulation around the duct (with blown in insulation) leading to condensation. A cavity tray has a much higher chance of catching mortar droppings bridging the cavity completely. the difference is a tray has a weeper to allow the moisture out. All i am saying is that's what's required for regs to do the job properly, with diy you can do what you like and your pipe may be fine who knows. 1 Link to comment Share on other sites More sharing options...
Mr Punter Posted October 14, 2021 Share Posted October 14, 2021 1 hour ago, Dave Jones said: All i am saying is that's what's required for regs to do the job properly No, NHBC just recommend it as best practice. IMO it was included without any real evidence or thought and the risk outweighs any benefit. Can you point me to any evidence that having a sleeved vent through a cavity wall has ever caused any damage, let alone the "thousands" you mention? Link to comment Share on other sites More sharing options...
Dave Jones Posted October 14, 2021 Share Posted October 14, 2021 1 minute ago, Mr Punter said: No, NHBC just recommend it as best practice. IMO it was included without any real evidence or thought and the risk outweighs any benefit. Can you point me to any evidence that having a sleeved vent through a cavity wall has ever caused any damage, let alone the "thousands" you mention? dont think there is anymore to add. Link to comment Share on other sites More sharing options...
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