Adding drainage holes above catnic lintel

25 Aug 2010
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United Kingdom
I have a 21-year-old bungalow of timber frame construction with brick skin. Condition is generally good all round but on one catnic lintel there are some early signs of corrosion on the outside edge; at present this is very minimal and you'd have to look hard to see it, but it was noted in the building survey when I purchased earlier this year. This lintel happens to be on the most exposed gable end of the building.

There are no weep holes or open perp joints above any window and I am wondering whether it would be a good idea to introduce some. I discussed this with a knowledgeable window installer and he was of the opinion it would be a good idea to drill some weep holes just above the lintels, taking care not to damage the lintel. I presume that I could do this by drilling on a slightly upward angle and then raking out the soft mortar with a screwdriver or improvised hook.

My fairly limited research suggests that a new installation would have weep holes at 450 mm centres, as shown here:

My questions:

1) Should the lintel have been fitted with weep holes?
2) Should I retrofit some form of weep hole?
3) Would an 8mm hole be sufficient, or should I rake the whole perp joint to provide ventilation?
4) Would there be any benefit in fitting a plastic weep hole vent, and if I do so, how would I retro-fit it in place? (silicon / friction?)

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