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Yeah, they are pretty slow to be honest. It's been over a week now since I sent them my window schedule and still no quote from them. They have at least acknowledged my email, but it is still pretty poor when i have stressed to them at the outset that I am in a hurry and need the windows urgently. I've also gone off them because they can't actually provide the product I want or something similar to it.

This is a good question and something that I have been pondering. The whole house has been gutted completely and we are installing new windows throughout (without trickle vents) and replastering, retiling and effectively redoing every single surface. I'm also putting in a wood burning stove which will be sealed with a pipe connecting it to the outside for intake of air. There is a gas fireplace that I will have to temporarily seal with a metal (fireproof) lid so that it is airtight when not in use, but that still leaves the issues of making the walls, floors and ceilings airtight, which I've read a lot about on this forum. I only learnt about MVHR after I agreed the contract price with my builder, so haven't had the "air tightness conversation" with him yet. Keeping in mind almost the entire ground floor will be a solid slab with either a polished concrete floor or a porcelain tile finished floor, am I right that there are unlikely to be any air tightness issues from the ground floor? We are also soundproofing the entire party wall at ground floor level so that we are no longer blessed with the neighbours' TV whenever they watch it (which is virtually 24h a day!). As for first and second floor, these will be built up with rockwell between the ceiling and floor, then a 6mm layer of rubber iso mat, then water based UFH (first floor only) then engineered wood planks or if I've run out of money by then laminate such as quickstep. So with all these buildups I'm not expecting a great deal of leakage. I expect you will say that I need to tell the builder to seal all possible joins/gaps with sealant and/or tape. I haven't included that in our contract. Is it likely to add a lot to the project cost? To give you an idea of sizes, here is a table setting out floor areas and volumes: GROUND Floor area height volume Zone 1 31.53 2.7 85.131 Zone 2 35.56 2.7 96.012 Zone 3 14.47 2.7 39.069 Unzoned 5.7 2.7 15.39 FIRST Zone 4 23.3 2.5 58.25 Zone 5 11.92 2.5 29.8 Zone 6 10.365 2.5 25.9125 Zone 7 15.93 2.5 39.825 SECOND zone 8 15.205 2.5 38.0125 zone 9 16.36 2.5 40.9 Total Area 180.34 Total volume 468.302

The facing bricks we are using are "fully frost resistant" apparently, but the engineer has specified engineering bricks below the DPC. It's a two storey extension, so needs to take quite a lot of weight.

So did you and @ProDave ignore the bit in the specs that says not suitable for extracting from bathrooms? Or maybe that's limited to this iteration of this model.

This one https://www.bpcventilation.com/mitsubishi-lgh15-rvx?gclid=Cj0KCQiA6t6ABhDMARIsAONIYywxIlW6CPGkPqQ3nsbvoN58-Uuo_c8WXffGujQ2IyYvX4iTg6IVFnoaAmetEALw_wcB ?

Thanks @joe90. Apologies if I've asked you this already on another thread, but which unit did you go for?

okay, thanks. What about covering the bricks in between ground level and the dpc with some form of damp proof render/cement?

I've only just realised (thanks to a comment by @joe90 on another thread) that ideally my unit should be placed centrally. This was not my original plan. Oops! This is what my loft floor looks like (or will look like once the builders get around to converting the loft later this year): In case it's relevant, this diagram is shown with: the party wall with the attached neighbours at the top (north); the street is to the right (east); a side passage at the bottom (south) between my house and my detached neighbours; and my garden is to the left (west). I had planned on siting my MVHR unit mounted against the external brick wall in the eaves storage that is to the bottom right corner, as this is: close to all three bathrooms in the house (one is directly under the eaves storage and the third is directly under the bathroom shown); the same side of the house as the kitchen (which is under bedroom 4 but out a bit into the garden (where we are extending at ground floor) not adjacent to any bedrooms or living spaces, so won't disturb anybody. But if the unit needs to be placed centrally, then this really isn't central at all as it is in the corner of the top floor of a three storey house. Another option is to place it in the larger Eaves storage space that is on the other side of the stairwell. That is more central although further away from all the wet rooms and very far from the kitchen. There is also no external brick wall there to mount it to other than the party wall, but that would defeat the purpose of mounting it centrally. I work from home in the "home office" most days (even before the pandemic) so the idea of having an MVHR unit so close to me is not something I'm keen on, because I have stupidly sensitive hearing and will probably hear it. That room also doubles as our guest room, so not great for guests either. The other option is in the utility room on the ground floor, that is up against the same external brick (southern) wall, but I thought it needed to go close to the roof. Any thoughts?

What's the ideal length for radial ducting?

Thanks @Temp I also thought that engineering bricks weren't usually visible; but in discussing it with the builder today he said that the DPC is 6 inches above ground level and that all bricks beneath the DPC should be engineering bricks. Looking at the engineer's drawings, that is consistent. But I'm having a french drain filled with pea shingle around the perimeter of the property, so I would have though those 6 inches will be covered with pea shingle. We started building 3 weeks ago and it's only over the course of those last three weeks that I've come to realise that our plans weren't detailed enough...

Sorry for the stupid question, but structural drawings are specifying Class B and the brick colour I have found which works with my scheme is available as a Category 30 or 50. So I'm confused.

Thanks @MJNewton, that's helpful. Could you clarify what you mean by "Attenuation of the ducts (for balancing)"? Sorry I'm a bit of a novice with this. What exactly is attenuation of the ducts for and is that a particular feature of the Titon HRV1.25 Q Plus, or can all units be set up that way? Thanks!

Trying to finalise my choice of MVHR unit. My main concern is to get something that is as quiet as possible. I know quietness is as much dependent upon the quality of the installation and where it is installed, and I think I have that covered in that I am hoping to install in the corner of my loft space, mounting the unit on an external brick wall, and that space is not adjacent to any bedrooms or living areas (it is just adjacent to a bathroom). But surely choice of unit plays a factor as well. Amongst my research I came across a Duco unit sold by BPC called the Ducobox Energy. What apparently makes this unique is that it has a two-zone system. BPC describe it as follows: A huge factor in the quietness of the system is that 2-zone system, as it reads where you are in your home and what needs ventilated you will not notice the system working. For example, at night, the unit will extract from areas such as your kitchen that are not being used, which ensures that the habitable rooms at that time such as bedrooms, will have no noise disruption. I had thought the best way of setting up the two-zone system would be for bathrooms, utility and kitchen to be zone 1 and the rest of the house to be on zone 2, as this would address my concern that whenever somebody had a shower or boosted to clear cooking smells, the unit's boost would be heard in the bedroom. We also run our tumble drier in the utility room overnight, so don't want the boost to kick in from that being heard in the bedrooms. However, on further research it appears that the zones need to be more "geographic", i.e. by location of the room rather than by its function. As the bathrooms are on the same floor as the bedrooms, segregating the bathroom ventilation from the bedroom ventilation probably isn't possible. It would however allow me to segregate the utility and kitchen from the bedrooms, so it would at least address part of my concern. Does anybody have any experience of this system?

The Vent Axia Sentinel Kinetic Plus B is one of the units I'm considering for my house, so I'm keen to hear: how long after you had it did it start to make this noise? whether you managed to fix it and if so how much was the replacement fan motor. BPC supply them with a 5 year warranty, so hopefully this is an issue that only occurs after 5 years, but curious to hear your experience. I'm also considering the Komfovent Domekt R-450-V, which is supposedly better (BPC sell that one for about £600 more than the Vent Axia Sentinel Kinetic Plus B) but the Komfovent Domekt R-450-V only comes with a one year warranty, which really put me off and is making me think the Vent Axia is a better bet.

Yes, but this structural engineer also wanted me to inject my foundation bricks with a chemical DPC. He's a great structural engineer, but not sure I'd follow his advice on other matters!

What make and model boiling tap do you have @ProDave and does it really provide boiling water? I always thought some struggled to get over 92 degrees.

I also live in London and have this exact problem. Builder dug trenches in my garden for our extension’s foundations and also did some trial holes internally to check how low we could drop the floor of the existing house before we ran into the corbels, and both the trenches and the trial holes filled up with water. Structural engineer initially thought it was a high water table. I called a surveyor who inspected and assured me that was impossible, pointing out that I live halfway up a hill. It’s just London clay, lots of rainwater and not enough trees to drink it up. Builder isn’t bothered about the water. He has a pump to suck it out so that he can get on with laying the foundations. But I’m still hoping February will be drier than January!

What dictates whether or not one should include a buffer tank?

Don’t you toggle the boost switch every so often or is that all automated? What about at night when you want it to run more quietly?

Thanks @troggy02 thats v helpful. What make and model unit do you have and who did the install and design?

In my search for a 1000mm by 2000mm flat rooflight I came across the Atlas range as one of the cheaper options that still looks quite good (at least on their catalogue). Yard Direct are selling them, including a kerb, in the colours I need and with a "free" upgrade to neutral solar control glass, for £1k inc VAT. This is similar to roof maker, quite a bit cheaper than the prices I've got from Sunsquare, and slightly more expensive than glass squad. Though it's not clear to me if glass squad and roofmaker includes the upstand, I think not, so probably price is equivalent to glass squad and actually cheaper than roofmaker. So my question is, where does Atlas lie in the hierarchy of rooflights compared to say sunsquare, keylite, roofmaker and glass squad? Is it good quality, or best avoided? I haven't mentioned Velux and Fakro because I don't believe they make flat skylights in the 1000mm by 2000mm size.

@Bitpipe I’m thinking of getting a stone resin bath from Lusso as well as a couple of basins and showers, maybe even a toilet. Are you happy with the quality a couple of years on? Did you go for Matt or gloss finish? I like the Matt, but some reviewers say it’s hard to clean.

True, but at what cost in the future. Obviously these guys have a vested interest in selling new tiles, but even so, some of this must be true: https://www.wienerberger.co.uk/tips-and-advice/roofing/what-are-the-risks-of-using-reclaimed-roof-tiles.html

I don’t understand. For what?

Yes, despite the odd leak I’m now wondering whether I should avoid retiling the roof. Found out today I need to underpin 4m worth of wall, so we are officially now over budget (blew my contingency on the sliding door and windows)! Need to cut back on something, but is skipping the roof a false economy given builder is already doing the loft conversion?