New Roof = Major Humidity/Damp in House

[JohnD]

I have concrete subfloors on the ground floor of which i know there is moisture in at least one section.

Is there a pipe buried below? Or a nearby drain?

 

[TNDU]

I don't know if this will help but we had a first floor flat in London (it was the top flat). We decided with the other 3 joint freeholder in the block to put in loft insulation. Unfortunately that created a lot of damp in our flat as the warmth from the property could not escape through the roof and the flat did not have sufficient ventilation. Insuffient ventilation in the flat wasn't a problem until the loft was insulated. We lifted the insulation and it helped with the damp but of course it meant there wasn't much loft insulation!

So it could be that the old roof was poor and so there was plenty of ventilation in the roof through it being old and so air was getting in from the outside in plentiful, but when you had the new roof, it was more air tight and so the hot air from the property gets trapped because there is a lack of adequate ventilation in the property, which was never a problem when the roof wasn't so air tight.

I had a house in London where the roof was old and the felt had fallen apart in several places. You could see outside light in the loft so there was lots of air flow coming through but when I got a new roof, it was pretty air tight and you could not see daylight any more when you got into the loft.

It could therefore be simply that your property does not have adequate ventilation, which has now become more obvious that the new roof is no longer acting as the ventilation for the property.

 

[RrogerD]

I don't know if this will help but we had a first floor flat in London. We decided with the other 3 joint freeholder in the block to put in loft insulation. Unfortunately that created a lot of damp in our flat as the warmth from the property could not escape through the roof and the flat did not have sufficient ventilation. Insuffient ventilation in the flat wasn't a problem until the loft was insulated. We lifted the insulation and it helped with the damp but of course it meant there wasn't much loft insulation!

So it could be that the old roof was poor and so there was plenty of ventilation in the roof through it being old and so air was getting in from the outside in plentiful, but when you had the new roof, it was more air tight and so the hot air from the property gets trapped because there is a lack of adequate ventilation in the property, which was never a problem when the roof wasn't so air tight.

I had a house in London where the roof was old and the felt had fallen apart in several places. You could see outside light in the loft so there was lots of air flow coming through but when I got a new roof, it was pretty air tight and you could not see daylight any more when you got into the loft.

It could therefore be simply that your property does not have adequate ventilation, which has now become more obvious that the new roof is no longer acting as the ventilation for the property.

I think that this sounds exactly like what could be occurring

 

[Harry Bloomfield]

I have concrete subfloors on the ground floor of which i know there is moisture in at least one section. But it isn't enough to be causing damp furnishings by far - only condensation build up on the windows if it gets cold. The house seems to be fine as long as you don't breathe or do anything (i.e. live) in the house.

As I say, it had it's minor condensation issues before the new roof but was otherwise fine and as soon as new roof put on, ka-blam. I know it's all supposed to be separate spaces between roof/loft and living space but there absolutely must be a link otherwise I wouldn't have had this.

Something is just not right here, it makes no sense at all.......

The loft area, and the living areas, are two completely separate environments. The loft, if vented normally, will quickly match the humidity of the outdoors, as it is intended to do, unless the loft area, is wide open to the living space....

I constantly log and automatically record my home's living area humidity, plus temperature, as I have done for several years. Normally it varies between 50 and 70RH, though it can occasionally get to 45 to 72RH. I have no damp, no signs of damp, no feeling of damp whatsoever. Temperatures, indoor, are usually maintained between 14C as a minimum and 18C.

My home is unoccupied at the moment, so my heating system is set to come on at <8.5C. I have just checked the indoor temperature, and humidity remotely, it reads 17.6C and an RH of 52.

 

[RandomGrinch]

Could therefore be simply that your property does not have adequate ventilation, which has now become more obvious that the new roof is no longer acting as the ventilation for the property

This has been my argument since posts #10 and #13.

Improving your roof, may have simply highlighted the existing issues from downstairs, that may have escaped notice before, due to poor sealing and insulation - this may not be the new roofs fault!

Unfortunately, it's so easy to see the damp being as a direct result of the installation of the new insulation, when the true cause lies elsewhere.
After all, warm moist air is more buoyant than cooler drier air - physics means it's unlikely that loft humidity would cause any issues with damp and humidity downstairs - unless there were noticeable leaks, or condensation causing damp insulation; factors that the OP has denied.

 

[JohnD]

Of course, the water will be coming from somewhere. A house does not create water.

 

[qwertyuiop1]

So another update and touches upon some of the further posts:

Had someone else around who said that they didn't think I had enough exhaust. The dry ridge in theory should be enough but clearly there is a problem. They ended up fitting a total of 6 tile vents yesterday and I immediately felt a different airflow yet again in the house. I was about to go out and say something to the guys and as I was on my way to the door, they knocked to say they were done. They seemed to think I had enough soffit baffles (total of 11 for an 8m long roof) for the system to work properly but said that they would be happy to come back and re-look at. My understanding is that you need a 50/50 balance of intake and exhaust ideally though it's always better to go overboard on intake than exhaust as if not enough intake, the loft exhaust will start pulling from the living space. I will monitor.

Interestingly they did say that the pointing needs to be redone on the chimney. So there is likely a source of moisture in general and need to speak to my neighbours as it's a shared stack. I will be doing that tonight. The flashing is absolutely fine and said that the roofing job itself that the initial roofers did was very good. So that's at least something. They also capped the fascia at the back of the house and installed new gutters. The fascia still has life in it so now will just remain as is....

We also inspected the house more generally and found a plugged up airbrick at ground level at the front of the house. We went around the house to see if there were any others that were plugged and there were zero other vents including in the small L shaped extension. I have unplugged that ground airbrick for now and will monitor. If it messes something else up I can always plug it back up.

Another interesting point: I have one of those smelly things that you plug in. I haven't been able to smell it at all anywhere in the house including in the room that I have it in. I used to be able to smell it in about 50% of the house. I can now smell it in the room that it's plugged in as well as the small cloakroom next to it (the air is flowing in the wrong direction ideally but again, will monitor).

The humidity in my kitchen seems to have reduced at least for now (my boiler is now reading levels between 56-59% as opposed to 60-64% RH - nothing otherwise changed on the thermostat programming) though I still have higher than I would like levels elsewhere in the house. That said, I was able to sleep without running the dehumidifier last night which I've not been able to do since the end of Sept and felt more comfortable this morning when I woke up (still too humid for my liking but not as stale as it has been. Will see what happens later tonight). Will continue to monitor and aiming to have the pointing fixed ASAP....just hoping the neighbour will cough up their share.

I still need to get the original roofers back to fix the membrane they broke at minimum (they were going to install over fascia vents as well).

I'm posting these updates in case anyone has a similar issue.

 

[qwertyuiop1]

Separately the small extension the people before me did has always had poor airflow. And after really inspecting overall ventilation yesterday, I wouldn't be surprised if it needs some extra help at some point and am looking at various options - I know a dMEV may be a good and cheap option but also looking at multi purpose dMVHRs (considering the Blauberg atm as can switch between different settings which may be useful). But first up will need to be repointing the chimney stack....