Decking + Damp Issue inside

[mj62mj62]

Hello,

Thank you in advance for your help with this.

I bought this house with existing decking. It is secured to the house and sits on top of an old stone patio.

We have damp coming inside. The damp is directly above an air brick, as shown in the pictures below.

I removed some of the decking and found that:

- Most of the decking has a 5mm gap between the ledger and the house
- Where there is damp inside, there is no gap. This is in the 2 corners of the deck.
- In those corners, some of the wood was black and flaked away easily. Is this a sign of trapped water rotting the wood? (see picture below)
- There are 2 airbricks

Is the missing gap causing the damp inside? Perhaps by pooling water in the corner?

I'm assuming this is all above the DPC. This is a raised decking that is 6+ feet above the garden and is 2 ft above the original stone patio below it. (there is another decking level and further steps not shown in the picture)



Pictures (note, it had rained as I was taking the deck up).

Overview:

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The problem:

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Is this rot?

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High Res 1:

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High Res 2:

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The question is:


How do I fix it?



My ideas so far:

Idea A - Silicon seal the areas where there is no gap. This will hopefully mean water flows away, but could it mean the render soaks up the wet?

Idea B - Flashing Tape against the wall and onto the ledger (L shape) so that water flows away from the building?


I'm not an expert builder so advice is greatly appreciated - thank you,
Matt

 

[Burnerman]

Only my opinion here but I think this deck is bad news......it is effectively preventing ventilation through the air bricks, and any water running down the white render is pooling at deck level instead of being cast away by the flare at the bottom, causing rot and damp ingress.
Sorry to say this, but if it was mine it would have to go.
John

 

[mj62mj62]

Thanks Burnerman

That was my original thought also. From what I've read, some people think it's fine that decks are installed above the vents because so much air moves underneath. They say that if damp were accumulating below the deck it would become a wet swamp - and mine is all dry... That may not be 100% proof of air circulating under the house though...

Even after heavy rain today there is no pooled water in the stone patio beneath.

Still you could be completely correct that the deck should be lowered and thus exposing the vents. The symptoms (damp) only appear in-line with these 2 corners where there is no gap. So I'm hoping to avoid deck surgery and to try to fix the corners first. Any thoughts on that?

shock: If you think I'm bonkers and am risking structural integrity or something, please let me know!! )

 

[Burnerman]

I think for sure, ventilation through air bricks has to be compromised in this particular case. The more air that can pass through them the better - the suspended timber floor will appreciate it too!
Although there doesn't appear to be pooling water under the deck, it doesn't look too wholesome down there! It's for certain that leaves etc will gather there and retain moisture.
If rain hits the deck, it will bounce above the DPC level.....this isn't desirable either.
Have you lifted any floorboards in the vicinity of the deck and wall? Damp problems can take so long to show, that anyone who recommends deck above DPC is long gone.......
What would the property look like, do you think, if it was reverted to the original stone patio- or does the deck have to stay?
John

 

[mj62mj62]

Thanks again

Inside the original floor boards are covered in fitted tongue & grove flooring so I have no way of seeing them. I could pull out some skirting and try to check that way. Let's see what I can do to check that...

 

[Burnerman]

Much better to see the floor joists direct, I think......ah, the perils of laminate!
Seriously, the more air that can circulate down there, the better - and there is evidence of damp affecting the outer leaf of brickwork. It's quite possible the cavity wall is breached with fallen cement, and this damp can happily transfer to the inner walls.
At this time, the decking isn't helping things where it touches the wall at all.
John

 

[mj62mj62]

If rain hits the deck, it will bounce above the DPC level.....this isn't desirable either.

I think the whole top level of the deck is above the DPC (I'm not an expert but I would assume so?).

I will take a photo tomorrow to show how the deck is on 3 levels and really makes the garden a lovely place to be on a sunny day. Sitting on the warm deck in the sun is fantastic

The lower 2 levels are below some other air vents.

What would the property look like, do you think, if it was reverted to the original stone patio- or does the deck have to stay?
John

We would like to keep the deck look (although re-oiling it is another conversation, i wish I had stained it or something instead)

Any decking can get leaves underneath, but is your point that having the deck below the air vents is the most important thing? The stone patio below would need completely re-doing to make it level enough to have a lower deck on top of it... (maybe with steps down from the french doors? this could cost a few £££)

 

[Burnerman]

If the property was mine, I would want to see all of the air bricks exposed and clear, so they can do their job.
Ideally, any bouncing rain shouldn't encroach above DPC either.
Looking at your pics again, the deck isnt helping matters much!
John

 

[mj62mj62]

Thanks Burnerman - with those few boards removed it is drying out now but I can see how much moisture it has been holding there... It is not proper decking and since changing it will be £££ anyway, perhaps it is time to get it all dug out and lowered.

Lowering will mean steps - a very strange setup having two doors and two sets of steps going down... it will reduce the useful amount of decking space out there.

If I had loads of cash I'd just get the house extended over that area

 

[AronSearle]

The problem is that it is difficult to quantify the amount of ventilation needed or blocked by that decking.

It will somewhat depend on what is on the other side of the house, how exposed both sides are and how much air is likely to blow through the under structure.

The joists and decking structure should be spaced off the wall by at least 10mm, narrower boards means more gaps = more air flow as well.

That the joists have decayed after 4 years shows they are both in a badly detailed situation, but it is also likely that have poor levels of treatment.

I don't think it is a complete non starter to have such a decking above the air bricks like you have, but I wouldn’t ever be enthusiastic about it.

 

[WabbitPoo]

As above. I'd be surprised if you couldnt prise the frame away from the wall enough to insert some spacers, just to get it away from the wall. I'd also run the deck boards away from the house (ie new boards).

To be honest I'd take it all out and replace it. It'd be easier

 

[mj62mj62]

Thanks WabittPoo I will attempt to unscrew the bolts and prise it away.

This is peak season for decking experts... The next time I can get someone is October!!!!

So I'm looking at temporary measures. My list so far:

(1) Try to prise it away from the house by undoing the bolts and attempting to insert spacers.

(2) Someone recommended thompson water seal and just coat the whole area until the deck can be redone.

(3) Someone else recommended silicon sealant and flashing tape

Any recommendations to last me 8 weeks and hopefully protect me from more damp?

 

[AronSearle]

(1) Try to prise it away from the house by undoing the bolts and attempting to insert spacers.

Make sure the spacers are near the bolts, I suspect you will find this hard to do as the deck boards will tie the whole lot up.

(2) Someone recommended thompson water seal and just coat the whole area until the deck can be redone.

All that will do is protect the deck board surface, the biggest risk is the end grain abuting the wall, as this will promote decay in board ends (assuming as well that they were re-treated when cut to size).

If you want to preserve the deck boards, pull them up (are they screwed?), cut them so they have 10mm clearance from the wall, and aggresivvly re-treat the cut ends and use an end grain sealent.

If you do this, you may as well try replacing/spacing the joists.

(3) Someone else recommended silicon sealant and flashing tape

Nope.

The next time I can get someone is October!!!!

CoughDIYFORUMcough.

 

[mj62mj62]

Done! Here are the results:

Prying - it didn't move. The 3 ledgers are attached to 3 walls with numerous bolts and all the ledgers and joists are nailed together. It bent a little bit, but no where near enough.


So what I did was:

(1) Cut off approx 10 inches of ledger on one side and 4 inches on the other out of the corner area. This was the ledger that was touching the wall and the wood that was a bit black

There are bolts close by and there are supports underneath the deck, so the deck is still very well supported.

(2) Did my best to get washers in-between the remaining ledger to create more of a gap, but it didn't move very much.

(3) Put some wood preserver on the newly exposed ends of the ledger where I had cut them.

Results:

- All remaining ledger has a 2mm gap. Obviously not enough, but it will buy me time.

- With the ledger removed from the damp area, hopefully the damp inside will subside (it probably needs replastering, etc, and I can then check the timber floor...)

- The air brick in the corner is more exposed now. This can only help.

Burnerman, AronSearle, WabbitPoo - A huge thanks for your advice and the time you spent thinking about this. I can't tell you how much better it feels to have found the potential cause and aliviated it, at least under a professional can come and rebuild. Thank You Thank You Thank You!!!

Next step is getting a professional in.

 

[LlewellynThomas]

Hi,

I have a very similar problem with my decking, was wondering if moving it away from wall did solve your issues.

Thanks

Llewellyn