Problem inside my roof gable wall (now with better video)

stator

I've just done some tests and annoyingly if you manage to get 1280x720 recording working, the FOV is reduced, they crop the raw image and you get a high quality video with a smaller view. Wheras the 640x480 image they must just scale the raw image down and you get a full view but low quality.
Not sure I'd recommend this camera

stuart45

What's your next course of action? Do you think the debris in the cavity is causing a problem?

EachPenny

stator wrote: »

If anyone wants to see how Laing Easi-form houses were made back in the day:

Thanks for the videos, especially the archive one.... watching that you can see how some of build quality problems have subseqently emerged.

I'd agree that what you see in your videos is rebar, at one point you can clearly see a 'hook' end used for anchoring purposes.

The question is what has caused the rebar to corrode, whether it is still happening, and if it is significant. The fact you've got water dripping down to the door suggests the problem is some kind of leak at roof level.

Has the roof been replaced or is it original?

teneighty

It doesn't take much for mild steel to start rusting, it could just be interstitial condensation or carbonisation of the concrete. It doesn't have to be exposed to rain and damp.

That is one of the fundamental problems with all these types of thin wall concrete construction. You need a minimum of 50mm of concrete cover to fully protect the steel reinforcement but that isn't possible when the concrete member is only 75mm - 85mm thick. In addition all it takes is for the reinforcement to be slightly misaligned and it ends up very close to the surface and it is only a matter of time before the concrete spalls.

stator

One half of the roof has been relaid with a rubber membrane. The other half looks original. I tried to look at the verge, but couldn't see any obvious problems.


It was raining a lot yesterday, and so I looked through my holes in the loft but I couldn't see any water inside the walls, so I think the problem with the back door might be lower down the gable end wall.


I'm thinking of drilling a few more holes in the loft so I can inspect the rest of the wall, and just make sure the problem with the rebar isn't more widespread. If there aren't any other areas with the spalling concrete, then I guess I won't do anything.

dunroving

Completely off-the-wall question: Is this a chronic problem (constant wetness at the door), or is it acute (only worse when it rains/has rained)?

If it is chronic, could it be condensation-related? And if so, does your attic insulation stop short of the external wall? A structural engineer told me about a similar problem (wetness around a back door) and after eliminating all local possibilities (gaps in the door frame, etc.) it turned out to be due to insulation stopping short of the external wall. Humidity from a family breathing all day and other sources was rising into the attic through the ceiling, and then condensing in the attic and running down the gap in the cavity wall.

stator

No, it's only with sustained rain.


I honestly can't work it out.



There are a few things fixed to the outside wall, but I can't see how enough rain would run through those holes, even if they weren't sealed, which they are. I fitted a canopy immediately above the door, so not much rain hits the door from outside. It's quite a puzzle

teneighty

The external leaf of a cavity wall is not designed to be "waterproof". In exposed positions under severe rain conditions the external leaf could well become saturated and water start to run down the back of the outer leaf within the cavity. It is especially noticeable where rainwater run off is concentrated in a small area like under a window with an inadequate sill drip or below a leaking gutter.

As long as the cavity remains clear from obstructions that is not a problem. The water will just run all the way down the cavity to the bottom or hit any cavity trays above doors and windows and be pushed back outside.

The problems occur when you get debris in the cavity or poorly installed insulation which allows the water to bridge the cavity. We can clearly see plenty of debris in the videos. If the bridge is not complete it can just channel the water away from the outer leaf and then drip down the centre of the cavity.

The only way you can find it is wait until you get the correct weather conditions and try looking in the cavity at that time. With traditional masonry it is easier as you can open up a larger hole but the borescope should still work. You could try soaking the wall with a hose but it can be difficult to exactly replicate the necessary conditions.

stator

I think I'll drill a hole below the first floor floorboards above the doorway. Then maybe I can see what's above the door in the cavity. Although the insulation will probably make it impossible to see anything.