Ventilation behind timber-cladding over thermal insulation.

[David001]

My question is: should there be intentional, planned, gaps or vents along the top of a wall of timber-cladding, so that air and moisture rising up behind the timber-cladding can escape?  Or is a continuous air-gap around the bottom of the timber-cladding sufficient for ventilation?

 

Just above ground level there is a 25mm ventilation gap between my house's thermal insulation and timber-cladding, but there are no intentional ventilation gaps at the tops of the walls, close to the soffits.  I've assumed that air should be able to enter through the gap at the bottom, then rise behind the timber-cladding, and then exit via planned gaps or vents in or near the top-most board, close to the soffits.

 

A very good carpenter has just finished nailing feather-edged boards (timber-cladding) over thermal insulation which has been placed around our house (PIR boards, covered by "TLX Silver" blanketing).  The timber-cladding has been nailed onto vertical wooden battens 25mms thick, so that between the outer surface of the TLX silver blanketing and the backs of the cladding boards there is a 25mm ventilation gap from the bottom of the two-storey house up to the soffits.   See the photo of the thermal insulation with the timber-cladding being added over it.

 

To reduce the possibility of the boards "cupping", two steps have been taken: before the boards were nailed in place not only were their fronts painted but their backs also; and, secondly, the boards are nailed to the battens not only along their top edges but along their bottom edges as well.

 

I expected that the carpenter would make provision for rising air and moisture behind the cladding to escape in the area of the soffit.  But it seems that the top-most board may touch the underside of the soffit (blocking egress there).  And probably because of the somewhat "wonky" surface of the old house, the top-most board, which slips up behind soffit's fascia, is not always hard against the back side fascia, thus leaving a gap - which some creatures may use to get behind the cladding (and possibly damage the delicate surface of the TLX thermal blanketing).  Just above ground level the 25mm gap between the bottom edge of the bottom-most board and the TLX blanketing has been fitted with netting to stop creatures creeping up behind the timber-cladding.

 

My feeling is that to ensure no creatures can get behind the cladding, the unplanned gaps (marked in green on the photos) should be filled with black filler or black foam, and that every metre or two along the top-most board a couple of wide holes should be drilled and then covered with a rain-proof and insect-proof vent cover, to allow moisture and warm air to escape.

 

However on another part of my house, which was clad by its previous owners 12 years ago, I see that no provision at all was made in the area of the soffits for the escape of air from behind the cladding, and the external appearance of the 12-year-old cladding seems to be in good shape.

 

What do you think?  Should I request only that the gaps be filled to keep out creatures?  Or should I request that the gaps be filled and that vents be added to boards directly beneath the soffits?

 

 

 

Edited March 20 by David001
Improving order of photos

[ToughButterCup]

2 hours ago, David001 said:

....

My feeling is that to ensure no creatures can get behind the cladding, the unplanned gaps (marked in green on the photos) should be filled with black filler or black foam, and that every metre or two along the top-most board a couple of wide holes should be drilled and then covered with a rain-proof and insect-proof vent cover, to allow moisture and warm air to escape.

 

 

Could not agree more.

Here's why I agree.  And I can't say @Russell griffiths didn't warn me.

 

 

[Kelvin]

We have a continuous air gap at the bottom and top with insect/rodent mesh also at the bottom and top. Ours is board on board which naturally creates a big gap behind the cladding anyway. One issue we do have is at the window head where we don’t have any mesh. My plan is to use thicker stainless steel mesh bent to fit and pushed up into the gaps. 

[David001]

Many thanks, @ToughButterCup and @Kelvin.  After reading your replies and then doing some research online I have decided that I will request the builder to fill all the gaps, to ensure no ingress of any form of wildlife.  However, after having read that professional Canadian housebuilders don't believe in ventilating at the top of such cladding, and because there is no observable deterioration in the cladding that was added to my house's modern extension 12 years ago, I won't insist on vents being fitted to the top of the cladding currently being added to the other part of the house. 

 

@ToughButterCup, thanks for your photo of the damage done by insects.  I can't afford for any creatures to nibble into the delicate silver-foiled blanketing on the other side of the cladding.  How tempting it would be for them to snuggle inside it in the winter - and possibly break the thermal seal that is costing us thousands!

 

[ToughButterCup]

That's no insect @David001, that was a rat. Just the one. That rat is now a has been rat. An ex rat. An is no more rat. A dead rat. 

We are now armed with 3 tomcats, a visiting Terrier Rat Pack, poison boxes and a decent Weihrauch rifle with an expensive night sight. Our sheep dog will spend a happy hour or two digging any newbies out of their nests. 

In proportion to the damage that rats can cause, we just about break even. Which reminds me: agenda for today, blocking all recent holes bar one. And then a simple water, bicarb and acetic acid bomb in the  remaining hole. The resulting CO2 rocks them gently to sleep. I hope.

 

In case you're interested, 200 ml bicarb, 200ml acetic acid 200ml water in old plastic bottle. Screw top tight shut. Shove in hole. Block hole. Hard. The reaction causes large volumes of CO2. Bottle bursts. Rats nest flooded with CO2. Rats die ( lose consciousness first then die) or leg it elsewhere. Yes hit and miss, probably miss more than hit. No one technique works with rats. 

 

After the initial explosion, rats that escape from holes I've missed are fair game for Tess. And other canine guests. 

 

 

[David001]

@ToughButterCup, thanks for the clarification!  I know what you're dealing with.  We have had a carpet soaked in water due to a mouse wanting a drink out of a plastic pipe in a wall.  We have had an area of ceiling cave in due to a squirrel driving the lid of an attic water-tank onto the ball-cock.  Now we have cameras in two attics and are able to see how many times the blighters return to the bait before they "no longer return".  Come the summer I'll be on my knees at ground level around the exterior of the house to try to find where they are getting in, although last week I witnessed a squirrel using a downpipe to get himself from ground level to the soffit above where he disappeared, so I need to check all around the soffits as well, and then mesh all entry points.  It's a battle, isn't it?

[Alan Ambrose]

>>> We have a continuous air gap at the bottom and top with insect/rodent mesh also at the bottom and top.

 

+1

 

And it's a right pain to do it after the fact mouse...I used this:

 

https://www.ebay.co.uk/itm/354744433416?var=624078758378

 

[Mr Punter]

That TLX stuff is pretty flammable.  Try holding a lighted match under it for a few seconds.  Be very careful with plumbers torches etc.

[David001]

@Mr Punter, thanks for the warning re. the flammability of TLX.  I will hope we have no fires in the area this summer!

 

@Alan Ambrose, thanks for the link to the aluminium rodent mesh.  I am ordering some pronto!