Under floor air ventilation

[Jimhomes]

Hi all!

I’m currently over hauling a Victorian semi on the Isle of Wight. It’s had damp issues in the past and I’ve had to completely rebuild the lounge floor. During the process I’ve had to remove several bricks to drag out my cavity. I’m about to add the insulation between the joists and get the floor back on.

I’m not sure on how many ( if any ) air bricks I need under the floor.

I’ve looked online but can’t seem to get a decent answer!

Thanks in advance

 

[a twig]

This is generally provided by ventilators on at least two opposite external walls, with air bricks properly ducted in accordance with Chapter 6.1 ‘External masonry walls’. Where this is not possible, suitable cross ventilation should be provided by a combination of openings and air ducts. Ventilation should not be obtained through a garage.

Sleeper walls and partitions should be constructed with sufficient openings to ensure adequate through ventilation. If necessary, pipe ducts should be incorporated in adjoining solid floors, separating walls or other obstructions. Where underfloor voids adjoin ground bearing floors, ventilation ducts should be installed.

Void ventilation should be provided to whichever gives the greater opening area:​

• 1500mm2 per metre run of external wall
• 500mm2 per m2 of floor area.

In the case of timber floors, ventilators should be spaced at no more than 2m centres and within 450mm of the end of any wall.

From here:

5.2.10 Damp proofing and ventilation - NHBC Standards 2024

nhbc-standards.co.uk

 

[mardinor]

Nice exhibition of 'percussive engineering' tools...

 

[Jimhomes]

Nice exhibition of 'percussive engineering' tools..

.I’m having a smashing time

 

[Toby Newell]

Hi all!

I’m currently over hauling a Victorian semi on the Isle of Wight. It’s had damp issues in the past and I’ve had to completely rebuild the lounge floor. During the process I’ve had to remove several bricks to drag out my cavity. I’m about to add the insulation between the joists and get the floor back on.

I’m not sure on how many ( if any ) air bricks I need under the floor.

I’ve looked online but can’t seem to get a decent answer!

Thanks in advance

View attachment 11852

Yes. And as many as possible. Also, leave air gaps in pier walls to facilitate air flow, plus only fit insulation to the depth of the joist so as not to impede air flow.

 

[Jimhomes]

Yes. And as many as possible. Also, leave air gaps in pier walls to facilitate air flow, plus only fit insulation to the depth of the joist so as not to impede air flow.

I’m going to have two air bricks per wall ( on the walls that are not party walls ). I’ll have the same amount on the pier walls.. it’s not a huge space so I hope that’s about right ?

 

[Lacan07]

I’m going to have two air bricks per wall ( on the walls that are not party walls ). I’ll have the same amount on the pier walls.. it’s not a huge space so I hope that’s about right ?

that sounds fine, you won't need more than that.

 

[Toby Newell]

I’m going to have two air bricks per wall ( on the walls that are not party walls ). I’ll have the same amount on the pier walls.. it’s not a huge space so I hope that’s about right ?

Two is enough, you normally leave regular gaps in the pier walls, you dont fit air bricks and they wont be enough.

Airflow through airbricks from outside and to outside is facilitated by differential air pressure from different sides on the building causing a negative or positive vacuum, thus they do not need to be very large to be effective.

Airflow through the building itself happens via convection and mass air movement and so obstructions can reduce this by a lot.

Notice the gaps before we replaced the piers and after, quite a bit bigger than airbrick size by order of magnitude.