air flow gap under doors with mvhr system

[lizzie]

From what I can make out Building Regs Part F is saying that with an MVHR system internal doors should have a total of 7600mm air flow gap, the example they quote is for a standard size of 760 door the gap underneath would need to be 10mm.

 

Our doors are 838 and I have worked back that we would need 9mm gap under them if this interpretation of regs is correct.

 

 Huge gaps under doors is not an attractive prospect.. assuming it is correct do building control insist/inspect that feature and/or does it compromise the eficiency of the MVHR system if we were able to stick with our 4mm neat gaps.  We never close doors anyway.....

 

Anyone help?

[Jeremy Harris]

I made all our gaps 8mm, and TBH it doesn't look that out of place.  I don't even notice them now.  I did have one bathroom door that wasn't trimmed properly and only had a small gap under it, and it whistled a bit when closed.  I took it off and trimmed it and it's now fine.

[joe90]

Interesting topic as I am yet to fit my doors and have ( will have) MVHR, P.S. I hate doors dragging on carpet so a gap will be fine.? 

[lizzie]

@JSHarris thank you that sounds a good solution and I definitely dont want whistling!

 

@joe90 we have all tiled floors so much less forgiving than carpet.

[Gone West]

We have a 12mm gap under our doors over a hard floor. I wanted to make sure there weren't any draughts which could be created if the gap is too small. I think we are just used to having very small gaps to prevent draughts but when using MVHR in an airtight house the opposite is true.

[James H]

We have 15mm under the doors when closed, hard wood floors with slightly raised metal thresh strips to cover expansion joints.

We also find no droughts in our house, which is quite air tight. having said all that all our doors are open all most all the time.

I thought that it would not look to nice with a large gap under the internal doors, but with them all the same you do not really notice.

[pulhamdown]

I didn't like the idea of a gap under the doors.  I kept thinking of a young lad who'd outgrown his trousers.  Instead, I inserted a grill in the bottom section of the door, powder coated in the same colour as my windows.  I got the door supplier to cut out the section neatly.  I have tiled floors downstairs, and carpet upstairs.  

[Ferdinand]

Check the trimming margins do course. Some are very minimal.

[lizzie]

27 minutes ago, pulhamdown said:

I didn't like the idea of a gap under the doors.  I kept thinking of a young lad who'd outgrown his trousers.  Instead, I inserted a grill in the bottom section of the door, powder coated in the same colour as my windows.  I got the door supplier to cut out the section neatly.  I have tiled floors downstairs, and carpet upstairs.  

My doors are already hung so trimming is only option now.

 

 

[Ferdinand]

Still check the trimming margins. If you over trim the door may come to bits, and you would have to trim some more and remake the door bottom from the first bit you cut off .. removing a slice. If the bit where you weakened the last bit of door structure is too thin a slice, then the recreation is tricky.

 

I got overenthusiastic on the Little Brown Bungalow with high quality 20 year carpet underlay and we had to extra trim 2 doors. Fortunately they were the two with extra leeway due to opening sizes. All the others were nearly down to the quick.

Edited March 15, 2018 by Ferdinand

[Jeremy Harris]

Remember that you don't have to use the gap under the doors as transfer ducts, you can fit ducts in the walls to do this.  If these ducts are arranged like periscope ducts they will tend to reduce noise transmission, plus you can add acoustic lining to any transfer duct to further reduce noise transmission.

[Temp]

I think the MVHR inlet vents on our system are about 4.5-5" in diameter. That's an area of about 10-12,000 sqmm so it seems reasonable to need a similar size duct or gap between rooms?

[PeterW]

17 minutes ago, Temp said:

I think the MVHR inlet vents on our system are about 4.5-5" in diameter. That's an area of about 10-12,000 sqmm so it seems reasonable to need a similar size duct or gap between rooms?

 

Check the duct size as that is the flow and capacity threshold.