vents for cavity in timber frame

babybuilder

hi
I am in the process of a self-build and have recently got the outer block leaf plastered with K rend. The house is a timber frame and I noticed that the block layers have not put in any vents to ventilate the cavity between the timber frame and the block wall. I know that its critical to allow moisture to escape the cavity so as to prevent rotting of the timber frame. I would be grateful if there is anyone out there who could provide information on
1) the name of the vents that could be retrofitted
or the level of difficulty in fitting them
2)where they could be purchased

My other concern is the problem with drilling or adjusting the k rend as this cannot be patched up.
Thanks

Do-more

Hi BB

I was looking for these myself sometime ago and found it very difficult.

I have seen circular weep vents fitted to a development in Abbeylara, Co. Longford (they are about 1" dia.) so the wall could be drilled and the vents retro fitted.

Unfortunately I can't remember the brand name, in any case when I Googled it back then, I didn't find any trace of the company.

Sorry I can't be of more help, other than to say they are available, but from where I don't know!:o

ircoha

Babybuilder, would be obliged if u could describe how any wall vents in your house have been fitted so as the wind does not enter the fabric of the building through the insulation as a result of the outer and inner membrnaes being punctured to allow thw inner and our vents connect.
Thanks

babybuilder

hi ircoha
The house is a timber shell with 50mm insulation on the outside to create a warm wall. Then a 50mm cavity and then a 100mm thick block wall. The idea of the vent is to prevent moisture built up which would cause the wood to rot. The vent punctures the plaster and block wall but not the timber frame allowing venting of the cavity. As long as the insulation is tightly placed against the timber frame then there will be minimal heat loss. Inside of the the timber frame and between the studs there will be 220mm wood cellulose and then 40mm hemp filling the service void.

Mellor

I think he was refering to the room vents as opposed to cavity vents.
I assume your rooms are vented.

babybuilder

hi mellor
I'm using a mhrv system for internal ventilation. At the moment the airtightness membrane in being done. However, I'm very concerned about the lack of cavity vents and would like to fix this asap.

Hi Do-more
That is probably exactly what I'm looking for. Someone has just shown me a large 200mm air brick which is made of galvanised steel but as mentioned already, I've got a K-rend finish which is tricky to work with. My builder isnt taking much responsibility about leavin them out and claims the architect didnt show them on his drawings, one blaming the other! The search goes on.

Mellor

babybuilder wrote: »

My builder isnt taking much responsibility about leavin them out and claims the architect didnt show them on his drawings, one blaming the other!

Not a nice situation to be in at all. As for the drawings, the vents are quite small and may not always been drawn at some scales.
But they should be included in the specification document. If they are included here but not install, or not included here, it might clear up the problem.
Im not familar with K-render, so not sure what the problem or equally the solution is

Builderfromhell

babybuilder wrote: »

hi mellor
I'm using a mhrv system for internal ventilation. At the moment the airtightness membrane in being done. However, I'm very concerned about the lack of cavity vents and would like to fix this asap.

Hi Do-more
That is probably exactly what I'm looking for. Someone has just shown me a large 200mm air brick which is made of galvanised steel but as mentioned already, I've got a K-rend finish which is tricky to work with. My builder isnt taking much responsibility about leavin them out and claims the architect didnt show them on his drawings, one blaming the other! The search goes on.

IMHO builder is responsible whether vents were on drawings or not. BUilder is contracturally liable to build in accordance with good practice etc. Otherwise he could claim lots of things were not on drawings ie. door hinges, correct size screws etc.
If a specification was issued with tender docs. there woulkd typically be a clause to cover this type of thing. In ay event, most reputable builder would correct problem without questioning who is at fault. I wouldn't let him get away with it or he'll take advantgae throughout job. Merry Christmas.

250882

call your timber frame manufacturer, they'll get you the vents or at least the sizes and spacing, youll need one set at the ground level and one at the eaves, itll be very hard work fitting them though coz theres a lot of them. If its a self build then I'm assuming that the drawings you are using are planning drawings, probably with a planning drawings only stamp on them if this is the case then there is no point in chasing the architect. Your builder seems a bit lost, these vents are the fundimental difference between a timber frame and a blockwork building and would lead me to question if any of the other parts are missing like the firestops above all the windows and doors, the cavity closers around opes etc. I'm surprised that your engineer didn't spot this when they were signing off on the rising walls. My advice would be to get a copy of the homebond building manual and start checking up on your builders work.

ardara1

I was under the impression that Timber framed cavity were UNVENTED.

Yes weep vents were placed at the foot of the wall - but these do not constitute ventilation.

Cavities are closed at wall plate level.

If you're going to vent the cavity - you could be running into problems with the fire properties of the materials WITHIN the cavity.

Speak to the UKTFA in Scotland

250882

Anywhere there is timber as a structure it should be exposed to a constant flow of air. There is a 50mm clear air gap in the roof buildup for exactly the same reason. the cavity is to be bridged only around windows with a fire stop and where there are compartments internally a firestop should continue that bridge. A good sourse for timber frame is COFORD Woodspec. I do however admire the Scottish approach and if I were ever to build my own house I would definately use the sarking board detail.

babybuilder

Hi all
just an update re:vents

Thanks to Do-more, I got in touch with a company in dublin called Drillvent (www.drillvent.ie) who manufacture 1" diameter circular plastic vents which are like those screw off plastic wine corks but obviously bigger and longer. The builder has fitted them now - approx 3 ft apart along the botton slightly below dpm level and along the top 9" below the eaves. they are a clear plastic so aesthetically they look ok on a white k-rend finish.
The guy who I spoke with was very friendly and I had the vents the next day. Around 90c +vat each. Btw, the timber frame company suggested I put in large brick vents which wouldn't have worked as a retro-fit.

Do-more

Great stuff BB need to get some myself, link is www.drillvent.com (not .ie)

Do-more

Got the vents and went about fitting them today, just a few points which may help others.

My engineer asked me if they had agrément approval, so I contacted the company and was told that there is no European standard for the ventilation of the cavity in timberframe houses so there is no standard for any weep vent to be tested against.

For what it's worth, Drillvent did say that they are approved for use by Homebond and Premier.

Regarding the fitting of the vents, they are made of hard plastic and are designed to be fitted at an angle of 2.5 degrees upwards to prevent water penetration. Because of the hard plastic they are very unforgiving of any deviation from 2.5 degrees or for that matter from 90 degrees from side to side. The flang at the front of the vent cracks or breaks when poorly fitted.

There are probably issues with the service life of the vents in using a hard plastic for their manufacture but I would say it would be a fair trade off to make them a bit more flexible.

Driving a large drill whilst perched atop a long extension ladder 9" from the eaves with a bit of a wind blowing is not conduesive to pinpoint accuracy IMO!

Ladders are never the safest solution in any case, but I have issues with access for anything else. I would however reccomend to anybody that the best option would be to use a cherry picker or scaffold if they can at all.

Cheers

D-M.

sean_ie

Hi baby builder and DoMore

I discovered this old thread while searching for solutions to a similar issue I have with a timber frame house I bought 8 months ago. It was built in 2001 without any vents on the external stone block leaf, so the air gap between the timber frame and external stone leaf is not properly vented. I see you bought vents from a company called drillvent.ie. That website is no longer in use. Do you have any contact details for them or photos of the vents you retrofitted? When drilling the holes for the vents in the outer block leaf how did you avoid drilling in to the breather membrane on the outside of the timber frame

Thanks