Roof Question tiny Drips

mike33

All

Hope im in correct forum section.

Noticed last night when up in attic, tiny water drops all along the middle of one side of my house roof .

They appear perfectly in a straight line and dont see any water marks/puddle/damp patches on the floor.

I dont see any slate damage on outside (but need to inspect fully).

I just find it strange the way the drip forms perfectly horizontle along the roof almost from one side of gable to the other.

There is not a constant drip or any kind of drip (To be honest that i can see) from roof to floor (They just seem to hang as shown)

Below shows pic (only shows section of the drips)

Surely If it was a leek in roof it would be formed more in a single area not universally distributed in dropletts like below?

Any thoughts or ideas as to what may be causing this?

Thanks in advance

MildThing84

Happened to my attic this time last year. Hot air rising and meeting the cold. I had roof vents installed and it solved my problem but mine was much more severe than what you have pictured. Make sure you have enough air flow in the attic and that you havent eaves blocked etc. Piling up the attic (we are all guilty) reduces air flow too. Another thing you might look for, hot air escaping into the attic via light fittings and other gaps. This will cause the sweating too.

phelixoflaherty

Make sure the attic door is well sealed.

A run of masking tape it quickest

10-10-20

Looking at your photo I'm kind of thinking that this isn't the common issue with condensation as the drops are linear in position and there is a clear water mark at the rafter over to the right. I wonder if it's a weakness in the felt at that point. Is the moisture present after rain but not necessarily on a cold and dry day?

mike33

https://www.boards.ie/discussion/comment/121457840#Comment_121457840

With Ref to above only noticed it last night and it was a cold frosty day with no rain.

I will monitor going forward.

mike33

I'll also check ventalation in attic as described here also.

Thanks All.

10-10-20

At the end of the day there shouldn't be much if any rain hitting the felt anyway, it's there as a secondary barrier and the tiles should be the first protection.

Is there a velux window on the same roof face? What cardinal direction is the roof facing?

standardg60

https://www.boards.ie/discussion/comment/121457840#Comment_121457840

I imagine the linear nature is down to the dew point being uniform across the roof.

10-10-20

https://www.boards.ie/discussion/comment/121458941#Comment_121458941

I was initially thinking that it's almost too well defined for that. Looking again now I think it's the felt overlap which is creating the line where the DP differs. I'm thinking now that condensation is happening where there is only one layer of felt and that the line is where the felt overlap occurs. So the attic itself was warm & humid and the heatloss was coming in from outside (as it does), and the DP was reached on the single layer of felt before the double-layer creating the defined line.

OP is there is slight ridge where you can detect that the felt overlap starts at or around the moisture-mark? Example here where the overlap ends are shown as 4" where yours appear to be around 10" to 12":

standardg60

https://www.boards.ie/discussion/comment/121459522#Comment_121459522

Yes that makes perfect sense, looking at the pic again you can see the DP occurs at the overlap where there's a double line of felt.

standardg60

Anyway OP warm moist air is getting into the attic slightly too quickly, so as above increase the insulation and seal any obvious leakage areas.

10-10-20

It has also been quite still and very cold, so conditions are good for condensing within the roof-space anyway.

mike33

thanks all ..... yes i noticed this during the frost days we had.

Yet funny since the bad rain i see no drips.

So im thinking some kind of condensation due to hot/cold air mixing?

GreeBo

https://www.boards.ie/discussion/comment/121459522#Comment_121459522

Am I going mad or can we not clearly see the overlap point in the photo in a foot away from the condensation line?

I would have said it was a crease or something in the felt, but maybe more like a scratch on the outer face that we cant see. Its too perfectly in line and the rafter is also went at that same point as you mentioned.

Ventilation always helps a cold attic space, but Im not convinced just yet that this is a condensation issue.

10-10-20

https://www.boards.ie/discussion/comment/121494288#Comment_121494288

You have a point. Back to my initial thoughts then.

standardg60

https://www.boards.ie/discussion/comment/121494288#Comment_121494288

That is just one end of the overlap, where the top piece ends. We can't see where the lower piece ends, but it's further up underneath the top piece, possibly where the line of condensation is. The OP could probably fit their hand between the two layers to check this.

Incidentally, shouldn't the lapping be the other way round, top overlapping bottom?

GreeBo

https://www.boards.ie/discussion/comment/121494452#Comment_121494452

I dont follow you.

We are looking at the felt from the inside, so the top is over lapping the bottom.

The other side of the overlap will be even lower down.

There will an overlap outside that we cant see but it will be higher again, unless they are overlapping by 75% which I doubt!

standardg60

https://www.boards.ie/discussion/comment/121494508#Comment_121494508

Maybe I'm going mad too but no matter how many times I look at the photo it's the top piece that is slightly sagging there, not the bottom one

GreeBo

https://www.boards.ie/discussion/comment/121494534#Comment_121494534

Might be one of those half cross your eyes 3d photos, but to me at least, the bottom of the photo corresponds to the bottom of the roof. The lower layer is sagging at the top, but this is pretty typical and this section will be covered by overlap on the outside.

i.e. the darker layer is above and overlapping the lighter layer.

Actually OP, those layers of felt look completely different to me, was there some roof alteration/repair in the past?

chooseusername

https://www.boards.ie/discussion/comment/121494534#Comment_121494534

Bottom of pic is wall plate, top of pic is ridge, otherwise felt is on arseways.

3 layers of felt, bottom of pic is layer 1 which is overlapped by layer 2 with the condensation droplets. layer3 (invisible) overlaps layer 2 down to line of droplets. So double layers of felt except between top of layer 1 and bottom of layer 3. Warm moist air rises towards the ridge but the dew point is further down at layer 2, the single layer of felt. imo.

There's very little condensation as otherwise the tops of the rafters would be saturated and moisture would be dropping onto the loft floor. Should be easy to fix with ventilation.

GreeBo

https://www.boards.ie/discussion/comment/121502152#Comment_121502152

If it was due (dew har har) to the overlap, wouldn't it be equally along the single layer portion?

mike33

Hi all

Sorry for the delay inm replying, Xmass kinda got in the way.

Above makes intersting reading, most of which went way over my head 😉.

To anser some of the above

No roof alterations were ever made.

Felt is as per done by the builders of the house so im assuming it's correct (Probably my fault in so far as I took bad pic?)

Anyway, just to update, It looks to me like a ventalaition problem.

Its gone away for now => eventhough it has rained solid all over Xmass.

It only seemed to appear during the spell of frost we had.

So based on that Im going to assume its some form of condentation due to poor ventalation.

Thanks all for taking the time to advice me.

Much appreciated.

GreeBo

A simple thing to do is just make sure that any attic insulation is back from the edges of the roof. You want your attic to be cold and windy, this removes any condensation from the leaky warm house below. As such, insulation needs to be kept back from the edges to allow air/ventilation to come in under the eaves/soffit/fascia and blow around within the attic space. This is how cold attics (what we have 99% of the time in Ireland) are designed to work.

dathi

https://buildstore.ie/felt-lap-ventilator.html

you could try a few of these they are placed between the felt lap to increase ventilation