mjward

So although I've identified the right way forward from an work perspective, I'm struggling on the regulations side. Current loft conversion signed off as such by building control 20 years (by the standards at the time). If I add insulation now, it will require building control sign off again. Will I lose the status of "loft conversion" (ie habitable rooms) because they don't meet the current standards (despite all I'm doing is IMPROVING them with this work)? Unfortunately my local BCO is not being overly helpful on this matter.

Yup a flat roof from the inside, hard to see from the pic but basically behind the wood work is just the vertical stone wall extended to the apex of the dormer ie no ventilation the fireplaces themselves are seal. 3 of the 4 chimneys are capped and when I get this roof work done I will be capping the fourth (just using anti-downdraft cowls, i.e. allow some ventilation but blocks the rain)

You're 100% correct. Is currently a cold roof and was built on top of a house with lime plaster, open fireplaces and sash windows. It now has modern plaster, closed fireplaces and UPVC windows (albeit with trickle vents) ie a lot of that natural breathability is now gone so I'm thinking slate vents should be introduced. I've not looked at them in detail before and I see for the calculators of how many you need they require you to provide the "required airflow" but it's not clear how to work that bit out Unfortunately that was a decision I should have spent more time on 2 years ago when I gutted the house. I've now crossed the Rubicon and rooms are at the final decorating stage so will have to do without but given the rooms have the size to accomodate it, it's certainly something I really ought to have done. Would have made the rewire/replumb a lot easier with stud walls too! Now onto a new(ish) query, as nothing is quite simple... I have what I would describe as "decorative dormers" (there is probably an official term but I don't know it). Essentially decorative protrusions on the roof that I doubt planning permission would let me remove (conservation area & preserving the overall look etc). But I can't work out how they would be treated when it comes to adding insulation over the rafters. Would there be cold spots under these?

Definitely. My preference has been to "correct" issues with the building fabric such as introducing several of the items you list. That said, there is also merit in mechanical ventilation and suspect a combination of the two will be most economical. On a side note, I've never had Velux loft windows before and after researching replacements (as current frames rotten from years of condensation), I've seen that they have built in trickle vents. Up to the loft I go and lo and behold, they were all closed. Have opened them all and made a note of current humidity and will recheck in a week to see how it's fairing.

Missed this. Yes that is correct John but pending delivery that utility fan will be upgraded to the Greenwood one recommended and set to continuously run. Additionally I've changed the bathroom to continuously run. What is good is how much improved the humidity has become since I opened ALL the tricke vents. The first floor was often around 60% RH which is when the dehumidifier was set to kick in but about a month ago I opened all trickle vents and without changing any of the central heating settings, the RH has dropped to around 48% (and that's with my daughter moving down from the loft to move into her first floor bedroom ie with an extra common inhabitant on that floor)

Sorry I don't have a clue. I've purchased that Greenwood extractor and will replace the utility one with it. I've also changed the Vent Axia bathroom extractor previously mentioned to be on continuously. So it will be both of those on the whole time as the primary mechanical ventilation in the house (in addition to all trickle vents open)

Sorry one last point... Ground floor = utility room extractor (& AGA) First Floor = 3x bathroom/ensuite extractors Given it's the loft that is showing the effects of high humidity, will better ventilation in the floors below solve that issue? Or should the loft have it's own extractor? Thanks all for your help so far. Really have a much better idea of what to do now

There is an ensuite with an extractor, another bathroom with an extractor and a utility room with an extractor. All light switch activated with no overun timer and given the ensuite/other bathroom aren't renovated yet, those extractors are rarely used. I'm starting to think that the way forward is to change the utility extractor to the one Iceverge recommends and to set it continuosly running and eventually to upgrade the ensuite/other bathroom extractors to either have 60 min overun or be continuously running as well. Hopefully between those 4 that's house ventilation taken care of. Yes, basically the roof nearest in that picture is part of a 2010 extension to the 1906 original building. The extension has openings to the original on both the ground and first floor i.e. I view them as one from a ventilation perspective. The extension roof is properly insulated and uninhabited whereas the orginal is the one in question here and has the loft conversion. Was messing around with some of these U-value calculators and it looks as though I could meet the target values with 75mm insulation between the rafters and 100m on top of the rafters. Throw cross battons then yes I can't see me raising it by more than 150mm and hopefully as you say, their desires seem to be focused on energy saving that this dominates their thought process.

Because I've set the overun timer to 60 mins in reality it's probably closer to the dMEv figure. My only concern with it set to continuously running (i.e. lower extraction rate) is it's ability to cope during and after a shower as the reason I changed to that one in the first place was that the previous extractor just couldn't keep up and the bathroom walls looked like someone had sprayed a hose at them. You're right about the dehumidifier cost, its not far off 80p/day (I recently plugged it into one of those power consumption monitors), so would be good to reduce that. My only real concern about adding further ventilation is heat loss. At 4000 sqft and Edwardian construction, it's already costing a fortune to heat and I wonder if the saving of extra ventilation vs dehumidifier would be lost in incremental heating cost?

I don't know too much about it as was fitted by previous owners but I know there is a pipe on the Aga that has its own dedicated external inlet as per photo

Thank you so much for that, I've tried to address the points above. In the interim I'm doing more research on the insulation element, certainly feels like between and over rafters is the best solution when it comes to comfort/heating (although I don't believe it addresses the ventilation issue). I will play around with calculators but I'm guessing a flexible insulation between the 75mm rafters followed by 150mm PIR on top of the rafters will get me in the right U-value ballpark for building control whilst not being shot down by planning permission for excessive roof height increase.

Thanks all, to address the points raised: 1) bathroom has a high output & efficient extractor, I recently upgraded it and has certainly helped as well as changing behaviourial issues (making the family leave the bathroom door closed until the fan has done it's job 2) all windows in the house has (open) trickle vents. This has definetely helped with overall humidity in the house, although not a fair test with a dehumidifier running although latest readings are 34% Ground Floor 48% First Floor, 58% Loft. So all absolutely fine but...that's largely due to the powerful Meaco dehumidifier doing a wonderful job. 3) With regards to the continuous extractor fan, is that between the loft and external (i.e. fitted in the gable walls) or between loft and house below? The reason I ask is that earlier research had brough up a product called a Positive Input Ventilator (I believe Nuaire are the leading brand). From what I could tell this really helps with humidity issues although by default I would ideally like a non-mechanical/electrical fix due to future mainteance and running costs. 4) In terms of cost I look at it from a value perspective as opposed to affordability. My thinking is, I will have the slates lifted to fit/replace the underlay with something breathable i.e. with the sunk cost of that work, scaffolding etc, I'm thinking that the incremental cost of adding insulation will be as low as I'll get it. That said, I fitted the ceiling insulation myself so know the cost/time it takes to do and what I've learnt is that rarely is useful when it comes to judging what I will be quoted! If I can pay X to add insulation and it (1) makes the room much more comfortable throughout the year and (2) reduces my heating costs then on paper it's the way forward but obviously all depends on X and if it makes sense over a 10 year+ horizon. 5) To add to the insulation element, where it becomes complex is where it is applied. At 6'2 I can only stand up in the centre of the loft, move a foot either direction and it's a crouch. That's with 12.5mm plasterboard. Given the 75mm rafters give me limited "between" space for insulation, if I went below rafters (say 150mm PIR each side) it would pretty much render the space useless for me. But if I go above, I enter the unknown from a planning permission perspective given I'm in a conservation area and from what I read they really don't like roof heights being raised (not to mention the additional work to the ridge boards) Not that it's a complicated setup but I put this quick sketch together to easily visualise:

Oh it is but was done at least 20 years ago when the standards were much low but nevertheless even at that time it was done very poorly. My primary concern is ventilation/humidity i.e. given its a converted loft space and plasterboard etc isn't great for breathability, what should I be changing to allow the humid air from inside the house to ventilate in a way that doesn't cause mould etc?

No cavity to the walls (c1906 building) The side with the plastic sheet has this sheet on top of the rafters (fairly tight ie not much of a sag) then the roof batons and slates on top of this. No OSB. Definitely think adding a few slate vent tiles will show a decent improvement Re vapour barrier, the main walls are uninsulated, just plaster onto stonework. In the loft there is plasterboard to box in the eves area but standard plasterboard, no foil backed/vapour barrier on them in the roof. I think you're on the right track, get some PIR in between the rafters (allowing enough of air flow gap) but also take down the old plasterboard and fit foil backed insulated plasterboard to lose a bit of room space but should make big difference re comfort and humidity From the access I have, hard to sell if slates on counter battons as the ridge board covers the view from the side and the plastic sheet stops me seeing whats happening above it. I'm in a deep valley in Yorkshire so probably not far off the winds you've got up there Will do some more digging on cold/warm roofs but you're giving me a few good bits to think about and research Cheers John

Hi John Thanks for your response. Basically when previous owners did a loft conversion 25 years ago they put in velux windows on one side only, on that one side there is a non-breathable (thick plastic) membrane, nothing on the otherwise but yes, originally constructed as cold roof. Re current ventilation, looking at it from the outside and from the loft, I can't see where ventilation could occur, The loft conversion is full (i.e. plastered walls, velux without trickle vents, carpeted floors etc), can't see where air could escape/enter. I chucked in a few lap vents on the side that does have the membrane but not made much of a difference. The side without a membrane is boxed off at the eaves ie no access. Agree re vents/eve ventilation required although I'm with one roof not having any membrane I would have thought plenty of surface area for ventilation but it's not occuring and can only thing that's because of the loft being boarded up on the sides with plasterboard and no air vents etc. Glad you mention the ridge system, all this terminology I'm learning as I go but from what I can tell it already is a dry ridge system ie no mortar on the sides, just timber cappings so theoretically the roof is ventilated/breathing but once the humid air gets into the loft space I'm guessing there is no way for it to pass through the plasterboard and out through the roof if that makes sense. There is currently no PIR in between the rafters, in fact there is nothing between the rafters right now so could it be a case that the plasterboarded walls in the loft conversion need air vents added to allow the air to get to to the eaves and out?