Garden office - damp(?) after persistent rain

[mri_ice]

So I'm in the process of getting a garden office installed. It was put together two weeks ago, windows and doors have been in since last week and I'm currently waiting for the insulation and cladding to be done. Annoyed that it's not done yet, but also pleased because you can see things that would otherwise be hidden behind the cladding

So after a day of very persistent rainfall, I notice damp around the bottom of the uprights and some floor boards on one wall only (it's the weather facing wall and it did rain rather heavily). I've marked it out on one of the photos, it's the wall to the left. It looks like it's seeping in from underneath or behind, around the uprights and also part of the floor boards as can be seen in one of the photos. Difficult to pinpoint a source since there is vapour membrane inside. After the sun came out it dried really quickly.

I got in touch with the company today and can't make my mind up whether they're having me on or not. They are saying

1. weather proofing the building is customer responsibility through painting and attaching gutters
2. I quote: "What you are experiencing is perfectly normal. This is the treatment draining from the uprights and just requires the building to be aired. Pressure Treatment in the timbers may take a while to dry fully"
3. Joints or gaps should be sealed with sealant or mastic

Now 1) I have pretty much done. It has 3+ coats of paint on. Guttering is attached to the back (the wall that has the issues is one where the the gutter would run down at an angle - I don't see how guttering would even work in this case nor how it would help with the issue) 2) I'm really not sure on this one...I would have assumed that if that is true, it would have affected all walls, not just a single (weather facing) one. 3) There are some knots that I can fill (knot.jpg). I'm also tempted to put a line of silicone just above the damp proof course to avoid any water pushing in and up, although I think that's a little far fetched. (dpc.jpg)

My gut feeling is telling me that the explanation re "treatment draining" may not be...100% legitimate? ... but I'm by no means an expert so would be extremely grateful for some thoughts on

- whether the reason given for the "damp" sounds reasonable
- what other steps I can take other than potentially putting another coat of paint on to the weather facing wall, close all the knots with silicone and put a line of silicone just above the DPC to ensure no water is driven up....

I would really like to get this sorted before the insulation and cladding go on (and I won't be able to see it any more )...so really hoping for more rain in the next couple of days

Thank you for reading this and thanks in advance for any thoughts anybody might be able to share.

Martin

 

[SFK]

Mr Ice,

I do not know why you have the water marks where they are.
But I have a similar office and I would NOT put the bead of silicon where you suggest (above the waterproof sheet).
This is because on my office this is where the water leaves the building, and you silicon would trap the water.

On mine, their is the frame, the water proof sheet and the cladding (nailed through the sheet to the frame).
If any water then gets pas the cladding (knot holes, cracks that have formed in cladding etc), the water follows down the outside of the sheet and escapes at the bottom of my office to the ground.
Note that my waterproof sheet extends to the ground.
Every few years I fill any new knot holes or cracks that have formed in cladding with brown silicone.

Looking at your images, the fact that I can see some water stain on the floor boards, and on the waterproof sheet (I think to the left of the upright stud) worries me that water is perhaps entering from roof, of through where nail hole is attaching the cladding to the stud.

SFK

 

[Notch7]

I cant see that its the where the dpc is -that is below the level of the bottom framing.

most likely it is ingress through the cladding.

A weatherboarded house would have breather membarne on outside, then 50 x 25mm battens laid flat, then cladding. Any rain getting through the cladding would run out down the 25mm cavity.

On a shed type construction, that doesnt happen, there is no cavity -its the inside.

Get you hose pipe out and work your way up that wall -you will see if water is getting in anywhere.

I know the membrane should stop it but it could get through where the cladding is nailed on.

 

[SFK]

Notch,
Like the idea of the hose pipe... wish I had thought of that.
SFK

 

[mri_ice]

Thank you both! In this case it looks like the breather membrane is fairly flush against the cladding from the inside, i.e. when when I push against the membrane from the inside I hit the cladding pretty much ASAP.

I will give the hose pipe idea a go and see whether there is anything obviously coming through, thank you! I will also fill in all knot holes and look at the nails that hold the cladding in place. Some of them seem to have been driven in rather deeply (nail gun presumably), maybe there is water coming in through there.

I have an air vent on that side also (see photo), will probably put a seal around this so that at least no water comes through around there also.

Out of curiosity - I have two air vents, one either side. The one on the opposite wall has been pushed through the breather membrane fully so it basically terminates in the inside cavity that will be filled with insulation before cladding. The one on the wall in question here is still sitting behind the breather membrane - pushing it inward so any air coming through would not make it through the breather membrane. I assume the first one is correct - i.e. a hole cut through the breather membrane to allow for air flow in?

 

[mri_ice]

Eurgh.

So I went around the cladding again and made sure I filled up all the knot holes, nail holes and any cracks. Another two coats of paint for good measure. There is absolutely nothing obvious outside as to where water would be coming in and of course it's been nice and dry until today.

Not so much now - this is after four hours of rain.



All exclusively along the same weather facing wall.

The cladder is coming on Monday but I'm really not happy with having this cladded and insulated in its current state. Surely it will just rot with damp like this.

I still cannot make my mind up at all and see no evidence as to whether it's coming up from the bottom and coming down from the top. The top parts of the uprights are absolutely bone dry so surely that means it all seeps up from the bottom? But what could cause that? A defective DPC?

Any further ideas / thoughts very gratefully received.

Martin

 

[mctav]

I had a similar issue last year with a summerhouse, turned out it was rain splashing off the ground and underneath the base. I dropped a load of gravel to absorb the rain in a strip around the summerhouse and this solved my problem.

If i were you I would try to remove that DPC altogether or shove it right in past the cladding just in case that DPC is catching rain, either directly or from ground splash and sending it inbetween the building and the base.

Stu