Corrugated asbestos cement roof problem

Hi
I have an old garage with a corrugated asbestos cement roof. I've recently cleaned a huge amount of dead leaves, moss & general debris off of it (16 bin bags full).

I've noticed recently that the inside of the roof is damp, I think it's condensation, but could possibly be rain water seeping in through the old roof sheets? I'm not sure if the problem was there before I cleaned the roof, I suspect it was.

There is good ventilation at the front as there is a good gap in between the roof sheets and the top of the door frame. The roof was actually dry at the front and didn't start getting damp until a metre back.

At the rear there are a couple of vent bricks at the bottom of the back wall, one of which has stuff stacked in front of it.

If the problem is condensation would replacing some of the regular bricks at the top of the rear wall with vent bricks help improve the airflow & prevent condensation?

If not any suggestions? Could rain water be seeping through the roof sheets?

Thanks!

 

Thanks.

The roof is clean now already. I'm think it's condensation rather than rain water seeping in, because if it being dry at the front where there is better ventilation? Plus it hadn't rained for 2-3 days before when I noticed the damp and the roof outside was dry.

The roof inside was actually a little icy where there had been a frost night before.

If I do need to treat the outside though then would Thompsons Water seal sprayed on be any good? I know this is generally for vertical walls, but was hoping it would do for a roof too. I'm a little nervous about crawling on the roof to spread/brush on that other stuff!

 

Ok thanks. I'll look at that as an option.

Regarding condensation though, if it is that would the vent bricks at the back wall help?

I shall keep an eye on it to see if it gets damper after rainfall or not.

 

I removed the leaves & debris a while ago & it's been dry on top for quite a while.

 

Thanks, yeah I'll spend a few weeks checking it and if it's rain I'll give that stuff a go.

Think I'll try and improve the ventilation regardless. If I wanted to replace a couple of the normal bricks with air bricks is it just s case of tapping out the mortar around a brick, taking the brick out, laying a bed of new mortar, putting in the air brick then filling top & sides with mortar?

 

Hi,
Just a quick update on this.

I've been monitoring & checking the roof daily. With all this rain we've had it's been roughly the same, a little damp on the underside, but nothing major, no dripping, no excess of water etc. There was one small wet patch around one of the roof fixing nails, where the rubber seal/cap has failed, so I'll fix that, but generally ok.

However after last nights frost (and no rain) I went out there this morning to check and the roof is soaked! There's been quite a lot of dripping and there are lot of water drops along the ridges waiting to fall. There is also a fine layer of water covering the roof, I've attached a photo, doesn't show it that well, but it looks like morning dew.

So, convinced now that the issue is condensation.

As I say the front is quite well ventilated due to the gap (about 2 inches high) between the roof sheets and top of door frame (there is no condensation/damp at the front of the garage as a result). There are a couple of air bricks at the back, however there are right at the bottom of the back wall. I intend to fit a couple more of these air bricks higher up, at the top of the back wall, but what else can I do to improve ventilation and reduce the condensation?

Thanks!