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  1. Sometimes questions are raised as to whether it's worth increasing insulation levels and often there seems to be confusion as to what the "ideal" level of insulation is, or even what a "good" or "reasonable" level of insulation might be. I'm not sure whether or not the non-linear impact of improving insulation, in terms of the effect on the heating requirement, and hence running cost during cold weather, is widely understood. I've heard comments like "it's not worth improving the insulation from 0.16 W/m2.K to 0.12 W/m2.K because it would be 30% more expensive and only reduce the heat loss by 25%". Most of the time this is incorrect, because homes have heat sources all year around, from the occupants, incidental heating from appliances, solar gain and even pets (a medium sized dog is probably a four-legged 40 - 50W heater). So, I thought a really simple example might help some gain a better understanding of this non-linearity, and illustrate better why some are so evangelical about trying to improve insulation levels (and reduce ventilation heat loss, too, but I'll get to that another time). Let's build a pretend house, that for simplicity has no doors or windows and is a rectangular single storey box with a flat roof. For simplicity we'll assume it's on raised piles, with an air space underneath, just so we can use the same insulation level on all six sides and to make the sums simple. All I'm doing here is making a comparison, so this is a valid way of illustrating this effect. In our rectangular box house we have an average of 100W of incidental heating, coming from things like internet kit, a PC, a cordless phone base station, a TV, a phone charger, a few lights and a handful of intermittently used kitchen appliances. This is a pretty low figure - I struggle to keep our house background load below about 200W, without any lights on. The box houses two adults, giving out around 80 - 100W each and a dog, so lets say there is 220 W of heating coming from the occupants. The box also has a heating system that can deliver whatever power is needed to maintain a temperature of 20 deg C inside, and its night time, so there's no solar heating of the walls. Outside it's 5 deg C, a chilly winters night. This rectangular box is 10m long x 10m wide x 2.5m high inside, so has a total wall, floor and roof area of 300m2 and an internal floor area of 100m2, so fairly average in size (a bit bigger than our current 3 bed bungalow). So, we have a temperature difference between the inside and outside of 15 deg C (20 deg C - 5 deg C), an internal surface area of 300m2 and a constant incidental heating level of 320 W (220 W from two adults and dog, 100 W from electrical appliances and lights). First, lets see how much heat we need to put into this box from the heating system, if we have U values for the walls, floor and roof of 0.2 W/m2.K (K is degrees Kelvin, the same units as degrees Centigrade when only temperature difference is being compared): The total heat loss power, in Watts, can be calculated from the U value, the area and the temperature difference, so for this first example we get 300m2 area x 15 deg C temperature difference x 0.2 W/m2.K U value = 900 W. There is 320 W of heat coming from the occupants etc, so the heating system would need to deliver 900 - 320 = 580 W in order to keep the house at 20 deg C under these conditions. If this were by direct electric heating, then the heating cost would be about £2.09 per 24 hours. Next, let's see how much heat we need to put into this box from the heating system, if we have U values for the walls, floor and roof of 0.1 W/m2.K , in other words, we've made the insulation twice as "good", so might think we've halved the heating cost: The total heat loss power is now 300m2 x 15 deg C temperature difference x 0.1 W/m2.K U value = 450 W. This is what we'd expect, double the insulation effectiveness and halve the heat loss. However, when we now take away the incidental heat gain from the occupants, etc, of 320 W, the heating system needs to deliver 450 - 320 = 130 W in order to keep the house at 20 deg C under these conditions. If this were by direct electric heating, then the cost would be about £0.47 per 24 hours. So, by doubling the insulation level we've decreased the heating cost by about 78%, not the 50% that might have been expected. This is a very simplistic example, but it does illustrate why doubling up in insulation can give a far greater benefit than might be expected. It also shows why, when you improve the level of insulation you can reduce the heating requirement down to such a low level that for a lot of the time you don't need any heating. In that last example, turning on a few extra lights could heat this imaginary box home to a comfortable temperature on a cold night, whereas with only half the insulation it needs something that delivers 446% more heat.
  2. Thanks for adding me to the group. We have bought an old rural school (Mouswald) from Dumfries & Galloway Council to convert into our home (3 bedroom and add second floor to one side - not a mez). Some pics attached and are at the stage of drawing up the Building warrant. Currently at the crossroads of deciding on what's the sensible choices/solution for ventilation/insulation for the walls/roof/underfloor. Council maintenance practices have been just as you would expect (patch repairs to lime mortar with cement and silicone squeezed in to cracks in stone / tarmac partially blocking vents) We have planning permission / a bat plan / archeology watch required when we dig founds for a detached garage. Hope to do as much as we can ourselves as budget tight. Apologies in advance for any daft / repeat questions #WhatHaveWeDone #We'llGetThere
  3. Ages ago I wrote a spreadsheet for doing what-if comparisons to see whether it was better to invest in more insulation in the walls, roof, floor, fit better windows and doors, or fit a better MVHR system. Others have found it useful and I've been reminded that I've not re-posted it over here, so here's the latest version. It should be self-explanatory, you fill in the cells with your wall, roof/ceiling and floor areas, add the areas of each door and window, put in the U values for each and, if you can, get hold of the met data from the met office for your area (the data in there is for West Wiltshire, right on the border with Dorset). This isn't a thorough modelling tool, it just looks at heat loss fairly accurately but doesn't take into account heat gains, although there is a crude way of doing that by drawing a line across the seasonal plot at the point where you don't use heating and you can very roughly assume that anything above that line will be heating. Please feel free to ask any questions, but bear in mind I wrote it back when I was designing our house and haven't used it for a couple of years. so I may be a bit rusty. Heat loss calculator - Master.xls [edited to add latest version of the spreadsheet]
  4. Hey guys, thank you so much for letting me join the forum. What a great place to find honest, experienced opinions and information. I'm working on converting a garage into a soundproofed studio and need to work out some issues with insulation and particularly ventilation. The room is 19.38 square metres so suitable for a mini-split system, which also means fewer holes in walls where sound could leak. However, I can't find out whether this would satisfy Building regs. Ideally it won't have opening windows or trickle vents, and only has one door to the house's hallway (ie doesn't access fresh external air). I guess the alternative would be to have a constant air intake and out take with a heating/cooling system but obviously that's more holes, ducting and baffling. Any advice anyone has on this would be extremely useful. Thanks so much, Andy
  5. I'm viewing some flats just now (built 1970) for my 85 year old Mum and am looking for some guidance re ventilating the bathroom in the flat she's really keen on buying (Flat A). Sorry if this is a bit long-winded, but it’s the only way that I can describe the situation. I just need to know what my options are before I put the offer in.The property is in Scotland (just in case regs are different). The building is 2 storeys high and Flat A is a top floor property, with a flat roof. The bathroom dimensions are 7’ x 7’ approximately. There is a shower over a bath, loo and wash hand basin. If successful with buying Flat A, I would be taking out the bath and replacing it with a walk-in shower. The bathroom does not have any outside walls. It has been wet walled and a new ceiling has been installed and fitted with spots. The wall opposite the bathroom door is an outside wall.I know from viewing another top floor flat (Flat B) at the opposite end of the building that there was a horrible domed skylight in it’s bathroom ceiling. This could be opened by putting a pole into a tube attached to skylight, thus ventilating the bathroom. I’m presuming that this set up is the same as that above the new ceiling in Flat A.Back in Flat A, through the bathroom wall on the side opposite the long edge of the bath, is a deep walk in cupboard accessed from the hall. In this cupboard, at the far end, it has been boxed in (floor to ceiling) with wet wall. There are two square holes cut into this (about 4”x4”) set about 4 feet and 4.5 feet off the ground, but the holes are not aligned one above the other. They’re offset by about 4”. The Estate Agent thinks that's where the stopcock might be located. Being completely non-technical I didn't even think to check. There is a hatch to the roof void in this cupboard, but as far as I’m aware it’s not a very high space, so don’t think a person could get up inside it to work in it.Through the wall, at the short end of the bath, is a shallow linen cupboard. This is also accessed from the hall and contains the shower's (over the bath) electrical switch.Can anyone please provide any suggestions (not horribly expensive) for the best way of venting the bathroom. For example, could a ceiling fan be installed with some sort of ducting running across the new ceiling and roof void to the wall outside. Would simply fitting a fan on to this outside wall be of any use, by at least removing some of the moisture that will come out the bathroom into the hall? I would be employing a company to do the work, probably the same one who would replace the bath with a walk-in shower. Look forward to receiving the benefit of your knowledge 😃🤞
  6. Hi folks. I am helping my old Mum buy a flat and am looking for some help with bathroom ventilation, and possibly other issues, if the sale goes ahead. I will post about that in the appropriate forum shortly, so appreciate being able to tap into your collective knowledge and advice. We're in Bonnie Scotland 😁
  7. I need to improve the ventilation of my own house (2009 chalet bingalow conversion, done to roughly 2010 regs), as it now needs to run slightly warmer for parent comfort reasons and is starting to feel a little stuffy (need to check humidity). In theory I could fit an MVHR, but it is a warm roof chalet bungalow conversion so that would be more than a little complicated, and also of course it would be a big disturbance. The plan is to try: 1 - a PIV unit upstairs - which will be on a wall on the landing not a ceiling with the unit in a space behind a stud wall in the roof angle, as nearly all the ceilings are sloping and if I get into the tiny roof voids it will be very tricky outside. 2 - Replace both upstairs and downstairs bathroom fans with (100mm) dMEV fans. 3 - If necessary trim a few mm off bathroom doors. I would welcome any comments. I am not expecting a transformation, just an improvement. I routinely fit PIVs in rented properties, and a HR fan somewhere downstairs, and all of the installations have worked well. Any comments would be most welcome. Cheers Ferdinand
  8. This weekend is MVHR install weekend (hopefully). We are looking for some pointers from anyone who has installed a Vent Axia Kinetic Sentinel unit. BCP has supplied all the kit. Very thorough. Could do with an idiots guide for the plan of attack though. First attempt at a plan. How does this sound? 1. site manifolds 2. Site plenums 3. Cut duct lengths and join between manifold and plenum (cutting holes in walls and floors as needed) 4. Site unit 5. Figure out how to connect all those silvery pipes from the unit to the manifolds 6. Put in pipes to outside Is this a reasonable approach? We have trawled this site for photos. Any out there that show all the connections to and from the unit itself and the manifolds? It looks like it should be fun (or the makings of a divorce) 😉
  9. Hello Members, this is my first post and I'd like to say that I really appreciate Jeremy's Heat Loss Calculator, which took one day to complete (yesterday). The compact one-page format with 'what-if' ability is very, very useful. Thank you Jeremy. These are my current considerations and I'd appreciate any comments and/or advice from members Regards, Hugh
  10. We need to put some insect mesh on our parapet roof edges. Got to allow ventilation into roof but stop the insects. Soon the parapet will be covered by a Sarnafil roof covering which will overhang, still letting ventilation come up but effectively weatherproofing the mesh. What sort of mesh would you use? Stainless steel (expensive but longer lasting) or plastic (cheaper but will it last?) or PVC coated woven fibreglass? Or something else? And will a staple gun do to fix it - if so, any clues on staple sizes? This is Saturday's job so going to need to order some stuff pronto. Sorry no photo - too dark to take one now.
  11. Have a look at this. Just about finished insulating between the rafters, and putting on the counter-battens. There are bits and bats of foam in the 50mm ventilation gap. Do I need to trim the foam flush with the top of the PIR? Thanks in advance. Ian
  12. Thinking of the current weather, can anyone recommend a secure way of holding a Velux Perhaps 50mm open when no one is home, or at night. Not a huge issue, but it is a little too close to next door’s carport roof for comfort. The window is a mid-pivot version.
  13. My house design has 2 deep, long balconies off the bedrooms on the upper floor. The decks have been designed with parapets; the build is by MBC Timber Frame and it will be a cold roof construction. The architect is doing all the necessary for building regs sign off and it's nearly there, but they are flapping about ventilation of the decks. Their concern is that the cold roof on the decks must be vented, but they don't want to put any vents through the vertical face of the cladding that will be on the outside of the parapet. As yet, I haven't seen the type of vent that they are trying to avoid, but does anyone have any other solutions for venting the roof other than going through the cladding? I've seen a few ideas where the air flow goes to the edge of the deck then up through the inside of the parapet, but I'm not sure if this would give sufficient air flow and achieve the necessary ventilation level. Any suggestions welcome.
  14. I'm aware of the basics of an MVHR install, that you want to keep everything balanced, you want to maximise the distance between supply and extract points, and that you want to extract from areas of higher humidity i.e. bathrooms and kitchens. My problem is that with a very small open plan house, I am struggling to find places to put the supply vents. I obviously want an extract in the bathroom, one in the kitchen, and I think it would be good to put one at high level in the loft space as that is where all the humid warm air will tend to go. These three points would end up as far from one another as it is possible to get. If I then had a single supply vent centrally located, that would maximise the distance between supply and extract points. But it's obviously not great from the point of view of keeping everything balanced. I'll try to attach some pictures of the house and a floorplan later.
  15. Just about to order some more PIR having sorted out my plan of attack. Half of this pitched roof is going to be 'vaulted' (i.e. Just one pitch of the roof with internal wall coming up right up to the ridge). So planning to fill between the 75mm (yes 75mm!) rafters with 25mm PIR and then a further 200mm PIR under the rafters. That leaves me with a 50mm ventilation gap. It's a slated roof with battens (not countered or any sarking) but have Tyvek breather membrane which I think means I could even reduce ventilation gap to 25mm? Build Reg Table 2 seems to say that roof u-value should be 0.18: This is a retrofit rather than new build but I want to get as good as I can get u-values and not simply satisfy BR! I've read so many conflicting roof values ranging from 0.11 to 0.2! Just need a sanity check that I'm on the right track here. Celotex calculator tells me I will end up with around 0.1 so with my EWI and 3G windows I am hoping i am on the right path. Everyone's specs are different but with BR values being pretty dire it's difficult to guage what a decent u-value would be! Should I try and improve on 0.1? I may be able to add a further 50mm but would mean fitting the plasterboard becomes a bit more cumbersome (Would probably have to fit battens underneath PIR and then fix PB to that).
  16. Evening all, Spent the evening taping the vcl & just finished off the evening doing some heat loss calcs and the calc surprised me. Background: Ceiling u value 0.09 Walls 0.15 Glazing 1.4 Timber frame, well sealed I'd say. Floor area 16m2 with volume of 41m3 (it is a high ceiling) MVHR. My calc suggests fabric heat loss of 180watts with the ventilation losses of 620watts. I assumed 2 airchanges an hour with -1 outside and 21 target, these two factors are responsible for the ventilation heat losses so are they reasonable assumptions? The calcs work out at a heat loss of 51w/m2 of floor area. I'm being rather ocd with taping etc so I'm hoping for a good airtest so if I achieve between 1 and 2 air changes an hour. I havent allowed for the mvhr or any heat rising from below (floors will have sound insulation which will reduce the heat rising from below). So do I need to suck it up or are some of my assumptions out? Thanks, CC
  17. Hi. I am a home ventilation specialist and work for BPC ventilation that are leading designers and suppliers of home ventilation and heat recovery systems to builders and self builders throughout The UK, Ireland and most other worldwide locations I will try to answer any questions and explain the facts from the myths Gary
  18. Hi, I am looking at further details for our planned bungalow to a house conversion. We will be adding first floor with a couple of bathrooms and bedrooms there. What I want to know is whether there is a requirement to have more than just a trickle/purge ventilation. The reason I am asking is I am contemplating whether to install standard MVHR unit or one of Fresh-R units with a view to install another one downstairs later as well. According to this I do not have to have mechanical extraction since there will be openable windows in bathrooms. Have I missed something? Any recommendations please?
  19. Excerpt from a previous thread. A member asked..... Following on from discussions regarding the desirability and availabilty of low output room sealed wood burners I have been looking at the alternatives. I need something that will satisfy our desire to have a "real fire" while at the same time having a controllable output of around about 2kW. Has anyone looked at using bioethanol burners as a compromise solution in this situation ? Do I need to make any special allowances for flue-less fires in the house or should a standard MVHR system be able to cope ? Are there any building regs to consider ?