G and J

We’re looking favourably at a Reverso unit, so v pleased to hear you say it’s quiet. Which variant did you use?

It will be me and I like the ply/holesaw thing for the ducts. I was intending to seek a proprietary grommet/gland.

And I am erring towards going that way, but trouble is I’ve soooo many other ‘just another few hundred £’ things I’m looking at and they add up. However raised tie trusses will be made from 100mm timber whereas fink will be 72mm so that’s nearly half again as much weight and that will all be manhandled up there.

That would push our ridge height up which means lower ceilings which we are looking at ways to improve. Noted. I think I need to play on paper with this to get my head round it. Upstairs is timber cladding on counterbattens on fire board on frame with 140mm PIR in frame and 25mm PIR layer inboard. Then service void and OSB inside fireline plasterboard. My ceiling VCL will be taped to the wall VCL, so if my tile underlay is taped to my wall breather membrane then the frame will be connected to the loft from a water vapour flow/airflow point of view. I guess that might be a good thing. Plus I won’t need to get a membrane under the trusses.

Simple pitched roof on fink trusses unless we go raised tie trusses for a little extra headroom in the house. No ridge beam, no vaulted ceilings. I see the attraction but it costs us headroom which we’ve not enough of and I think the time I spend doing a service void well will be greater than making it airtight - given that we’ve a handful (maybe 5 in total) downlighters and less than a dozen cable entries. That was my first thought. I still like the fact that it will be easier to get to below the walkway this way but (subject to cost) a PIR/board sandwich felt like the easiest to live with. Inspired! And we’ve a selection of windows to choose from sitting in the bungalow that will be demolished.

If I’ve understood you correctly then, it should work without significant condensation risk and if I seal completely with the right taped up tile underlay, etc.then I will see a tiny thermal improvement. If my periphery sealing isn’t perfect the loft will still be ok but I’ll not get the tiny thermal benefit. I like the sound of that, thank you. I’m surprised, given how often peeps have mentioned ‘air washing’ undermining insulation, that it isn’t more of an issue in the loft. But I also like the idea of a substantially bug free loft too. Our trusses will stop with their outside edge coincident with the outside face of our walls, so I’m thinking that I can do a truss version of a Tony tray on them to provide effectively a continuous air barrier from the VCL under the plasterboard to the tile underlay. I’m also hoping it will only ever rain at night lol

Good call. We’re intending Ergovent vents for aesthetic reasons, so I think the airtight seal will be to them above each room (I know that’s not what I wrote though, so it’s a very valid point). Very good point. Thank you.

Noted. Will keep looking but I like my ‘Thunderbirds’ type Heath-Robinson type mini projects.

I’ve mulled that over sooo many times. We are restricted on ridge height thence headroom (long and not entirely happy story). So to do that would mean raised tie trusses, adding between £500 and £1k to the build. I’ve toyed with the idea of doing that anyway to gain circa 3.5” of head height which can be done without chamfered ceilings (which I dislike), so it might be part of the answer. But I’m put off by the idea that I have a membrane above the ceiling that can billow in the wind. Can you imagine how irritating that might be? So it would need boarding under the membrane I think, and that would make future alterations really difficult and push the cost and effort up too.

I think that’s an inspired idea for warm lofts. Brilliant collection of the rising hot air to recover the heat from. If I knew of a sensible way to airtight a fink truss roof I’d want to replicate that.

Well done you, out of the ground so the biggest risks are now behind you. I’ll be unbelievably relieved when we hit that milestone.

So, thank you for these suggestions. Clearly I’m no further forward on whether my plan will cause me a problem with condensation, but let’s go with the idea of a warm roof and see where that leads…. Some background: Don’t want vaulted ceilings, just a personal style choice. And the increase in build cost and complexity of a non fink truss roof isn’t attractive. There will be a small number of downlighters upstairs, the plan was to put each under it’s own plastic flowerpot (AKA Loftlid). There will be a maximum of 6 no. 90mm flexible ducts up there breaching the airtight membrane. All emerge in one area and then they connect to each ceiling vent. Plan A also has a 4’ boarded PIR walkway down the middle and lots of easy to lay soft insulationy stuff down the sides. We are determined not to store stuff in the loft, like ever, but one does need access from time to time. Theres few rooms upstairs and so not too many switches and light fittings. Ugly but sealed loft access hatches are available and that’s the default, though I’m devising a better looking homemade one. Noted the shag of sealing up each of these but it made everything else so easy that it felt like it was worth it. I have chosen a cold roof because of the following issues: (I’m opened to be corrected/enlightened) If I go warm roof, I think my airtight layer becomes the vapour barrier under the insulation within the fink trusses. That means I’m taping up round many, many truss penetrations. I think this alone would be more time consuming than sealing round me wires and me ducts. I increase the amount of area to be insulated by a factor of circa 1.4. I think that means a lot more than 1.4 times the cost as it will be different insulation, which will require fitting, and it will require a lower u value to achieve the same heat loss as there’s more area to loose the heat. I think again this is more work than my ceiling sealing. I think part of the issue is that we are going for champagne spec on beer money. Airtight and fink trusses aren’t happy bedfellows. But that’s why I need the buildhub mind….

The plan is to have an airtight membrane above our upstairs ceilings, so minimal water vapour gets from the house into the loft. That will have oodles of insulation just above the ceilings. I really like the idea of NOT ventilating the loft, (like in the diagram), instead using breathable (water vapour permeable) membrane under the tiles to control/limit humidity in the loft space. Our architect has expressed concerns that condensation will form when the roofing membrane freezes. I think he’s not factored in the airtightness preventing steam filling the loft. Am I likely to have a problem?

We have three Clearview stoves, an 8kW connected to a 6’ insulated flue, a 5kW connected to an 6’ insulated flue, and another 5kW connected to am 8’ clay liner (this installation would not be allowed now). All work exactly the same, the control on the fires set how they work as long as they have a decent draft. When the fires are burning properly the flow rate is very small, which is what delivers their efficiency. We had a Dovre previously that simply couldn’t work like that and asa result used twice the wood. So I assume that the flue temperatures are much lower with my current fires than they would have been with an open fire or an inefficient stove. I think that means that whatever size liner you have if burning properly they won’t get that hot, so I see no issue in continuing with your 8’ flue. That’s certainly what I’d do in your position.

Would it have been more appropriate if I had started a new thread?

Hmmm, so that’s less than 6% of your budget… How much would a cock up cost?

Please tell me I don’t have to fit one of these on each of my bath and all the showers! We’re looking at a nice big hot water cylinder which can be heated to circa 50c to be nice and efficient for the heat pump.

Interesting discussion with our architect yesterday. I expressed my intention to have a cold but sealed roof à la @Iceverge. Reasoning: Loft to be non-habitable, cheapest fink truss based, very limited use for storage. Cold loft with insulation above plasterboard is cheapest and quickest solution. Hate insecty lofts, with a passion (as I’m now sitting underneath one, humph). Improved thermal performance. Fits nicely with airtight strategy as I’ll put a VCL directly above plasterboard ceilings. Yes I’ll need to faff around sealing round wires and MVHR ducts but I’m happy with that. So, the architect then mentioned a drawback: it transpires that he’s heard of cases of condensation forming under specific circumstances on the inside of the ‘roofing felt’ (I’m a wrinkly, I know it’s technically breathable tile underlay but everyone knows where roofing felt sits!). The circumstances are that it’s freezing conditions, roofing felt freezes and becomes vapour impenetrable, condensation forms. Hmmmmmm. Don’t like the sound of that. Now one of my less positive attributes is that I think very slowly, and hours later I realised that this may be a symptom of the architect not being as used to working with airtight house designs as they could be. My thinking is that if I achieve an airtight ceiling then little water vapour will reach the loft and thus little or no condensation will form. So, is that a safe assumption? Will a sealed cold loft above an airtight house have running water?

You can park two Citroen Amis in there. So it’s a double garage. What more do you want?

When I discussed this issue with my preferred MVHR supplier they suggested that the carbon filter be placed after the unit, so the cheap filter in the unit reduces the build up of crap on the expensive carbon filter, but also said leave room for it to be installed inline but leave it to see if it’s needed, as it isn’t actually needed that often. That works for me. And @Duncan62, I looked up that link, it says it’s a 420 filter. Are there lots of very relaxed people around your place? 😉

I reckon it sagged. They put the thin ply up and chucked stuff on it then panicked when they saw how it drooped between the rafters, hence the micro joists with half fitted hangers, a diddy ‘L’ bracket would have done. Would have been cheaper to buy a sensible thickness of ply in the first place.

But I agree with you re the comfopost. Feels to me like a bit of kit that sounds brill on the tick list and can bump up the invoice for a disreputable outfit but actually delivers little benefit to most houses. Interesting that the companies I’m talking to re MVHR kit have both strongly suggested not to bother with one, so full marks to each of them.

I don’t know the answers to those questions. So I’m going to try to allow for all eventualities where I can without wasting tons of money. I’m putting a Fancoil into our bedroom, with a drain and also insulated pipes to the manifold and room to allow isolation valves and a volumiser (that really is a word that should be confined to hair product adverts!) so that if the ‘above dew point’ approach isn’t enough we can reconfigure without ripping out walls. So, no immediate need but a bit of bet hedging.

Not applied, but have spoken to Hanley Economic. They were very helpful, but would be worth looking at their website as they detail what type of property they'll lend on.....our planning design of timber frame with more that 50% timber cladding did not meet their guidelines.

Just a cautionary tale from an oldie .....our first time round in the 90's we bought a plot with outline planning, when we went to full design it turned out that highways had not responded first time round, when they got the opportunity again they tried to stop the development, similarly this time round the consultation period was rerun and a couple of consultees who did't reply first time finally got their responses in, in the second window, all was ok in both cases but......it maybe worth checking that all the consultees did actually respond and what those responses were.