It never really emerged out of our bubble Tony. Not sure if that's because our argument isn't/wasn't strong enough, or certain parties have an interest in not allowing it.

I've noticed an interesting effect in my fairly-airtight house; the MVHR is not currently active (naughty) and though steps are taken to minimise moisture generation, and run a large dehumidifier I've been mystified by some apparent leaks that I see tracing down the sides of my bifolding doorsets. I know I have a couple of roof leaks that affect teh same area, the top of the frame of the door fills and then the water runs out at either end and presents itself at the foot of the door and runs down the wall (these bifolds are on the second storey)

Opening the bifolds to stick my head out for a better look, I see the gap between frame and door is chock full of beads of water. I presume this is due to bifolds not having an amazing air seal (particularly along the bottom) when they use a low profile threshold (it's basically a plastic leaf with bristles either side that brushes onto an aluminium runner, kinda like a draft excluder) and small amounts of house air seep into the cavity and then condense on the parts the other side of the thermal break


I'll be interested to see whether enabling the MVHR improves this

I think Tony is exactly right, the more we build tight the more we need to ventilate right as long as the more we do the former the more we must do the latter to maintain health ( and save money and the planet).

It pains me that building regs aren't up to speed on moisture. They want me to internally insulate a solid brick wall with some unfortunate concrete render on the outside. The outside has gone green (presumably condensation from the outside meaning the wall finish is both waterproof and soaking). Still haven't figured out how to do it without building a new wall or EWI.

Stove installer wanted a big hole in the wall to make sure the stove had enough air to burn. Why functional checks, CO2 alarms and the leaky doors and windows aren't enough I don't know.

It is environmentally friendly these days to rip out your perfectly good 100 year old windows and replace them with short lifetime windows with trickle vents...

Absolutely sensibly planned ventilation is important and surely much more efficient than adding random holes in the walls. Also the world is still mad.

Posted By: vordThe outside has gone green (presumably condensation from the outside meaning the wall finish is both waterproof and soaking).

Depends what direction it is facing. North-facing walls can go green whatever they're made from. Walls close to trees or other shade, likewise. But the average surface humidity needs to be fairly high, though not what I would describe as soaking.

Article on this subject in last issue of Passive House Mag. Perhaps that's what prompted Tony to post?

Airtightness is improving faster than ventilation is. I suggest that this is a transitional period. People will work it out, as we do actually know what to do (MVHR)

I think wookey has hit the nail on the head. It is fairly easy in a new build to insulate it well, and seal it up. The problem in this country is we live in a damp climate, so HAVE to ventilate out the moisture. I see a real need for MHRV type systems, but 99% of users will not understand how to use them properly, or maintain them properly. Loads would just turn off the MHRV, close the windows and trickle vents, and then complain about the condensation.

I think, in my gloomy moments, that it is a ticking time bomb.

IIRC a recent / last study showed MVHR works well, BUT occupants 'forget' to clean/change the filters,
thus the systems become inefficient = Daily Maul horror stories...

Djh, I know you told us but cannot remember where, what kind of post heater do you have, electric or wet, what size and do you find it effective for your build ( I have to plan whether or not I have one)

+1 for a heat pump rather than direct electric

Good plan

The UFH downstairs will take a long time to heat the slab overnight and hopefully last most of the day. The bathrooms only need an hour to warm the vinyl flooring and electric UFH is much easier to lay for a small area and short time needed.( IMO)