1930's Semi: sub floor and cross-party wall ventilation conundrum?!

[Safety First]

Situation:1930's Semi. Suspended wooden floors. ALL Air vents until recently blocked by concrete poured around both houses- raised ground levels etc. Underfloor party walls are perforate.

What to do?

My questions are :
1. Should I fill in the between-house ventilation? I.e., Brick up the x4 half bricks smashed out ( by who? when?) within our party wall?

2. Should I add a vent from an unused chimney direct to sub-floor to increase further the draw of air into our sub floor? My hope would be that more air would be drawn into sub floor from our air vents.
In our other (used) fireplace I have made a vent from the sub floor to ground floor to supply air to the wood burner ;not direct but withing 300mm from burner itself. This will pull more air into sub floor...


Background....
On moving in 5 years ago we took up the carpets and exposed damp sub floor with woodworm mainly to floor boards running against the external wall where ground levels were raised over DPC. Causes of water ingress/damp are now removed on our side- boiler not leaking, rainwater not running into ground (!) and ground level lowered below DPC, via a french drain. Damaged timbers have been removed and we've been drying out the whole house with dehumidifier and have increased air flow by having bare boards for 4+ years. I am imagining that our sub floor is drier now than it was. It has been very cold though, and we are looking forward to sealing off the air flow between ground floor and sub floor, albeit for woodburner floor vent and question 2 option venting chimney to sub floor.


I am about to lay ply and vinyl over ground floor and want to establish best state for ventilation before I lay new flooring and so leave the sub floor to vent/function 'on its own'.


In trying to sort out the bouncy floors I have repaired the brick piers and inspected under the floor. Along the party wall, the length of the house, there are two fireplaces. Either side of each chimney breast (under the floor) a half brick has been smashed out, so connecting our houses in terms of air flow. Is this normal?
There looks to me a microphone sticking out into our sub floor ! (kidding!).....

I believe that next doors air vents are blocked as ours were when both houses had concrete poured around for driveways. Chap does not seem to care about this. I talked about it all within a year of moving in and uncovering our vents.

So! ...
Does anyone see benefit in blocking off the ventilation between our houses given that they are not planning to remedy the raised ground levels and lack of air vents on their side? Are they not just bringing damp air to the party?

If I make their situation worse and dry rot occurs on their side, won't it come our way through the party wall- even with the 'between house' vents filled in?

Is there any reason not to try to increase air flow under the floor as much as poss?

Any considerations at all, very gratefully received.

 

[^woody^]

I'm not quite up to the Sunday essay read, but generally you need cross flow ventilation across the underfloor, and not vented into the house - their is potential for warm air to be drawn into the cold void. Air needs to be moved around in the corners too.

 

[Safety First]

I'm not quite up to the Sunday essay read, but generally you need cross flow ventilation across the underfloor, and not vented into the house - their is potential for warm air to be drawn into the cold void. Air needs to be moved around in the corners too.

That was a short post for me. For me it seems that many starting posts, and responses for that matter (!) often state the obvious/generalities or omit a great deal. At least you read (some of) it (?) and contributed. Thanks for the input, I had not considered that air from lounge might go back down under the floor and condense... Maybe I could make some kind of flap-valve thing... probably noisy and and a PITA to make...

What do you think about the business of connecting sub floor to chimney, to draw more air in?

And what about the party wall being perforate?

He he!

 

[Nige F]

That was a short post for me.

What do you think about the business of connecting sub floor to chimney, to draw more air in?


He he!

That worked for me

 

[Footsoldier888]

Regarding this gap between the party wall, this should not be happening as it will be a fire risk and is defeating the idea of a party wall as regards fire transfer.

As regards the blocked air vents, if it was me I would pay for a reputable damp specialist to do a report and then if you are suffering damage from your neighbour l would start thinking about legal redress after exhausting all attempts to talk it over with the neighbour.

However can't you fix your blocked vents first before tackling next door?

 

[Safety First]

Regarding this gap between the party wall, this should not be happening as it will be a fire risk and is defeating the idea of a party wall as regards fire transfer.

As regards the blocked air vents, if it was me I would pay for a reputable damp specialist to do a report and then if you are suffering damage from your neighbour l would start thinking about legal redress after exhausting all attempts to talk it over with the neighbour.

However can't you fix your blocked vents first before tackling next door?

Thanks for your post. I have fixed my vents now, those that I can find. Odd thing is, and this has occurred to me since my original post... I now think that the house was designed with cross flow across the houses- using the party wall vents. The front of both houses is a single skin of stone- no cavity. Both houses have on their sides, two vents each. Ours are now unblocked, their are blocked. There are no signs of any at the back though we have put on in under a patio door that we had put in in place of a bay window. So we have three working vents.
I am sure you are right re fire risks etc, but it would make sense that it was built this way, unless someone would have decided to get under the floor to smash out x4 half bricks across the party wall?

Good call on the damp specialist. Like you say, to get a professional opinion on basis of which to make changes.
Thanks again. I do appreciate you taking the time to comment/ help .

 

[John D v2.0]

I think gaps in party walls are reasonably common but wouldn't be allowed nowadays under current building regs.
In a loft they'd likely be picked up on a homebuyers survey and there's a good chance they'd be repaired at that point, but under a floor no one's likely to notice. Useful if you want to tap into next doors ring main
My advice would be to block them if it's easy enough, and concentrate on getting your through ventilation and stopping any sources of water under the house (ground sloping towards etc)