Air Brick Problem

[mike1978]

Hi,

I have a house which was built in around 1820 and then converted to dwelling in around 1920. In the main living room, there is a suspended floor and the front of the house goes out on to the street.

Today, i had to take some of the boards up to run some leads, but noticed the sub floor is a bit damp and bits of wood left around under the floor have that white rot on them with a general damp smell lingering.

At the front of the house are two very small air bricks similar to the attached pic which seem a little inadequate for the floor - about 18m2. One the air bricks is a bit blocked as it has a large plant box in front of it so i'll be moving that. At the back of the living room, the floor drops about 40cm to another room, so there is no way of fitting air bricks on the opposite wall - the floor just finishes in the middle of the house.

I'v attached a diagram of the house layout to show what i mean.

What would the best way to get some suitable airflow under the floor to get it dryer? Or are those two little air bricks going to be sufficient as long as they are clear?

Thanks, Mike

 

[bobasd]

Its possible & simple to insert ventilation such as 9" x 6" plastic air bricks in the 400mm step-down.

You need more air bricks at the front elevation and what about any side elevations?

When looking under the floor look for an intermediate knee wall.
All wood debris must be removed from the oversite.
Look for mushroom and plant growth.

Why not post pics of the front elevation, the step-down, & the underfloor white rotted bits.

 

[^woody^]

It's been up 200 or 100 years and there's no actual problem from what you've posted.

Clear the air bricks, that's it

 

[bobasd]

mike1978,
I look forward to seeing your pics.

 

[mike1978]

i've pulled the planter box out of the way so hopefully, that'll help. I'll have to see if i can get a pic of below the boards later on when i've finished work, but see below for the front.

Its going to be tricky to put vent bricks in the internal wall where it steps down as the wall is about 700mm thick and stone - it was once the exterior wall at some point. the kitchen floor at the rear of the house is part concrete and part suspended floor - its quite a frankenstein of a house!

Side elevations is sold stone to next door on both sides as we are a terrace. I did check next doors and one side has no air bricks (but i'm not 100% sure what their floors are inside) and the other side has one solitary air brick in the middle (similar layout to ours)

 

[mike1978]

Here’s the front elevation . You can see the two air bricks - i know the one on the left particularly is ground level which isnt great, but we dont get water pooling in this area that i have seen - i think it runs towards the road.

 

[bobasd]

You are on a slope with ground water pressure coming downhill from left to right - with only two air bricks - you could insert two 9" x 6" plastic air bricks on the right hand side and replace the left hand 9" x 3" with a similar size plastic air brick. Plastic a/b's give more ventilation area.

What, if anything else, you should do depends on how much access you can get to the void to examine the condition of the joists.
Given that any existing front elevation DPC has been well bridged on the left front then If your joist tails land on that front elevation then you might have wood rot troubles there?

The thing is, that the flooring might be good enough for a number of years yet or it might be on the edge of degrading. Examine all the interior walls, esp the front elev. at skirting level, & test the floors for any movement.

fwiw:
At a min. the front render should be cut off 50mm above ground contact.
The kitchen suspended floor might also be at damp risk.
If the solid floor in the kitchen doesn't have a membrane (DPM) then it too is at damp risk.

 

[mike1978]

Sure, thanks - how come you suggest two sir bricks on right and then just replace the one on the left?

i probably need to take a closer look at the joists which will be cemented into the front stone wall. There is no movement in the floors at the moment but defo worth me checking - prob at the same time I look at what to do with the air bricks. There is no Dpc at all in the house - the walls are solid stone with lime cement so meant to breathe - I rerendered the inner wall with lime plaster which has helped but the exterior is normal cement I imagine.

The kitchen floor I had to take up completely and fit new joists across as they were rotting in the wall. There are no air bricks at all on this side though - again , a very thick 40-50mm stone wall. Again I removed all the cement plaster so the walls can breathe which has helped enormously- they are dry now whereas they were really damp before which is on reason fir the kitchen joists rotting out.

I did think about the possibility of fitting an extractor fan mounted under the floor of the lounge to help get the air moving - is that something to consider if the air bricks are not adaquete enough?

 

[bobasd]

There's no room on the left - go any higher and your above the FFL.
Originally, there would have been further venting under the door threshold, & the frontage ground level would have been much lower.

If the joists have been "cemented into the front wall", as you put it - then its almost a certainty that the tails are rotting - but you first have to investigate before any Remedial work.
If your dating is accurate you might find that floors have previously been replaced.
There are methods of dealing with rotting joist tails in wall pockets but i wont go into them here.

Note that suspended floors with no or poor ventilation dont need rising or penetrating damp to create damage - heavy and consistent condensation alone will cause a floor to decay.

When no other options were available for natural venting we have cut slots in floors and covered them with brass Hit-n-Miss cover plates - but doing this can sometimes bring along other problems.
I'm not a fan of sub-area extractors - but research them, and peoples experiences of them. They've been mentioned on here in the past.

Still waiting to see pics of the decayed wood debris?

 

[mike1978]

Here we go for pics - finally got done tonight

i really need to take a couple of boards up near the wall to see what the ends of the joists are like

 

[bobasd]

The pics show a crawl space thats par for the course for such a badly ventilated space - nothing sinister suggesting say dry rot for instance.
The wood debris suggests previous work, and in time it would be best practice to remove all wood debris.
Given the sloping site the sub area soil is remarkably dry.
There seems to be enough space under there for crawling around.

 

[mike1978]

Yep - we certainly get a lot of slug trails on the carpet in the mornings which my wife is convinced are coming up from under the floor!

I think I’ll probably stick done better air bricks in at some point and attempt to clear out some of the wood debris aswell - hopefully tat might help with the dank smell that seems to emanate from there

 

[BumblingBees]

Hello! Is there any update on this? We are facing a very similar issue in our home.