Weep vents over lintel into what will become an internal wall

[James Duke]

Hi,

I'm planning on extending a room out through an external wall. I'll be putting in a lintel to create the opening. If the lintel was over an external door or window, i assume you would put weep vents in. But the wall over the new opening will now become and internal wall and will be boarded and plastered. I'm not sure how this works.

 

Thanks 

 

James 

[markc]

No need to weep vent lintels for internal walls …there shouldn’t be any water getting in or condensate forming.

[James Duke]

Hi markc. Thanks for the response. We are breaking through into an attached garage that was built after the house so the wall we are breaking through is a cavity wall. The garage roof is lower than the house roof so there is a short section of wall that is still exposed to the elements. Does that make any difference?

 

Thanks 

James 

[Mr Punter]

If the garage roof is lower there should have been a cavity tray and weep holes just above where the garage roof joins the house wall and this would still be in place.

[ETC]

https://nhbc-standards.co.uk/7-roofs/7-2-pitched-roofs/7-2-20-weathering-details/

[Gus Potter]

8 hours ago, James Duke said:

Hi,

I'm planning on extending a room out through an external wall. I'll be putting in a lintel to create the opening. If the lintel was over an external door or window, i assume you would put weep vents in. But the wall over the new opening will now become and internal wall and will be boarded and plastered. I'm not sure how this works.

 

Thanks 

 

James 

Hi James.

 

Hope this help you form a view on what approach to take.

 

I would imagine that BC throughout the UK generally follow the same principles when adding an extension as they do here in Strathclyde.

 

The first thing we do (as you have done) is to identify the wall type; solid brick, thick stone, brick/block cavity wall, brick/block with timber frame on inside and /or anything else.

 

If facing brick then when we add on an extension to say a two storey building or where we have exposed (to the weather) brickwork above we always retro fit a cavity tray, stepped for a pitched roof butting onto an existing external wall, flatish trays for a flat roof. The reason for this is that we know from bitter experience that water gets through facing bricks, particularly the perp ends (the vertical bit of mortar at each end of the brick) and also through the bed.. the type of pointing makes a big difference as it can channel water back into the cavity. Good weather proof pointing can look untidy or takes more labour time to execute.

 

The cavity tray serves to catch any water penetrating the outer leaf of brick. When water does, it runs down the inside face of the outer leaf. Also, you can get condensation forming in the cavity depending on how your insulation is set up. The tray catches this water and sheds it out through weep vents. Incedentally the weep vents can also help vent the cavity of say a timber frame.

 

To sum up the above.. when you add an extension to a cavity wall with facing brick the risk is high that you will get water dripping in over the new doorway to your extension. BC in our neck of the woods expect to see a cavity tray when there is facing brick. This makes sense.

 

However, if you have rendered walls then provided the wall above the roof of the extension is well rendered, in good condition, not too high and does not contain too many movement joints then BC are happy with a wraggled flashing into the outer leaf, provided it is well detailed and sealed. The render serves as a water proof layer. Now potentially you may get some condensation occuring in the cavity but for extensions BC are fairly pragmatic. I can't remember a case where I have been called to look at water ingress over a say a door slapping and found that it is due to condensation.. maybe because the walls are strapped out on DPC?

 

Now we need to apply some common sense. Have a look at how your extension faces. If at the head of a Welsh Valley prone to driving rain (80 -100 mph winds) then maybe fit a cavity tray. If in the cultured west end of Glasgow and well sheltered with a rendered wall then probably ok with a wraggled flashing.

 

If you look about your own area you will see loads of extensions with wraggled flashing, no retrofitted cavity trays. On a new build the NHBC will always insist on a cavity tray but that is understandable.

 

If in doubt drop your BC officer a note and just ask what they will expect to see detailed. Or you can post more detail on BH, maybe a drawing, info on the wall type, what direction it faces and how much wall is above the new roof of the extension. This may be enough to let you form a crystalized view?

 

 

 

 

[James Duke]

Thanks everyone for your responses. I'll have a look at the garage roof tomorrow and see if there are any weep vents where the garage meets the bungalow