does treating timber really help that much with , wet/ dry rot

some supplier in my area (SE UK) only stock treated structurial timbers and many drawing I quote on
specify treated timber through out , which I generally ignore. I believe most timber treatment by suppliers
is just a way of upselling , increasing profit on a standard item.

If you got a leak ,it'll show on a ceiling or something and you fix it

as for insulation blocking air flow at the eaves you can use those corrigated vent things( rafter tray)
which are a good idea anyway as they let you stuff the insulation right in to the eaves and hopefully help get over the problem of eaves/wallplate/wall insulation being the week point

http://www.klober.co.uk/product2.php?id=15

thank mike , good info

how about wet rot , how does treating timber (if it does) help there

Mike the most severe timber rot incidence I encountered was actually wet rot . A concealed valley gutter for its entire length was reduced to looking like a Cadburys Flake . Acro- props dig out and replacement works followed . The replacement wall plate was pressure impregnated as were the the spliced joist and rafter feet . This Victorian terraced property was neglected - the valley gutter sole was perished . The vendor concealed the rot by fresh skim and decoration . We suspected we may encounter some rot - but not to this extent . The property was purchased in the desperate "take it or leave it" atmosphere of the dearly departed boom time .....

My view is that so much of the argument against judicious use of preservative ( meaning wall plates , sole plates joist and rafter ends ) is predicated on the basis that a building will always receive due care and attention . But they don't always .

I don't accept that because the OP's timbers have never suffered rot that they never will . It is , in the near future I assume , going to be heated and insulated like it never was before . Perhaps for most of its life it did not have a sarking felt . Lots of air flow . The existing 70mm Rockwool ( assumption - based on not knowing the built detail) most likely is not covering over the wallplate and rafter ends . It may not even approach the tops of the joists . So as you have pointed out - plenty of these timbers surafce areas are exposed to free air movement so even if localized wetting events arose before - dry rot could not take hold .

The contemporary eaves detail - 300/400mm quilt which packs tight into the eaves pinch point must include a rafter roll vent strip . That vent strip will do nothing for those timber parts now wrapped in rockwool . No free air movement potential there . So what we have local to our eaves detail are timbers with hopefully a vapour barrier below , Rockwool pack and a PVC vent strip over which will form another local vapour barrier over the timbers . Now suppose water penetration occurs - and the building is neglected. What will happen ?

The OP - in my opinion - has a golden opportunity , when these timbers will be exposed for hopefully the only time in decades , - to minmise the risk of timber rot

Perhaps you should re read the 1st line of my last post . And please don't twist my words around . Or speculate on a building i saw and you did not .

Hardly a daft question . Fungal attack encouraged by excess moisture in timber is the common denominator with wet / dry rot . Preservatives delay / inhibit the process only - they can't stave it off indefinitely . I can't say for sure to what extent any treatment would be effective James . It would "buy time" that's all I can say . Several years I would hope to bridge periods of neglect - that's all .

Now the OP may well make a judgement that he/she will ensure that the building will be carefully maintained "on their watch" and that preservative is not required . Which may seem fair enough . But this Grade 2 listed building will pass on to others not all of whom may care for it is well as he/she will . The preservative may just be enough to "bridge" such lapses . Maybe . I would apply the treatment if it was my house .

Tony.

"Dry wood is of no interest to woodworm or fungal spores"

Is this true? I was not aware that woodworm was only attracted to damp or wet wood !! I found woodworm in my workshop bench and the timber has never been damp or wet (workshop is built to house standard ie damp course/membranes etc. I put the woodworm down to cross contamination from old wood stored in the corner which had the dreaded worm and I had not spotted it.

Posted By: sinnerboyMike the most severe timber rot incidence I encountered was actually wet rot . A concealed valley gutter for its entire length was reduced to looking like a Cadburys Flake . Acro- props dig out and replacement works followed . The replacement wall plate was pressure impregnated as were the the spliced joist and rafter feet . This Victorian terraced property was neglected - the valley gutter sole was perished . The vendor concealed the rot by fresh skim and decoration . We suspected we may encounter some rot - but not to this extent . The property was purchased in the desperate "take it or leave it" atmosphere of the dearly departed boom time .....

My view is that so much of the argument against judicious use of preservative ( meaning wall plates , sole plates joist and rafter ends ) is predicated on the basis that a building will always receive due care and attention . But they don't always .

I don't accept that because the OP's timbers have never suffered rot that they never will . It is , in the near future I assume , going to be heated and insulated like it never was before . Perhaps for most of its life it did not have a sarking felt . Lots of air flow . The existing 70mm Rockwool ( assumption - based on not knowing the built detail) most likely is not covering over the wallplate and rafter ends . It may not even approach the tops of the joists . So as you have pointed out - plenty of these timbers surafce areas are exposed to free air movement so even if localized wetting events arose before - dry rot could not take hold .

The contemporary eaves detail - 300/400mm quilt which packs tight into the eaves pinch point must include a rafter roll vent strip . That vent strip will do nothing for those timber parts now wrapped in rockwool . No free air movement potential there . So what we have local to our eaves detail are timbers with hopefully a vapour barrier below , Rockwool pack and a PVC vent strip over which will form another local vapour barrier over the timbers . Now suppose water penetration occurs - and the building is neglected. What will happen ?

The OP - in my opinion - has a golden opportunity , when these timbers will be exposed for hopefully the only time in decades , - to minmise the risk of timber rot

Been thinking about this. I don't think we're really that far apart in our views. I understand completely why you want to avoid any kind of risk, and if I came across your scenario I may well do the same as you. I guess there is nothing like first hand observation to make to make the necessary judgement.

Use a loose fill insulation product and this will eliminate any air gaps that could occur between fitted rolls of quilts. If a storage area is required then build a raised platform around the loft hatch area and insulate underneath.

In terms of installation guidelines for insulation in pitched cold roof structures these are detailed in BS5803:Part5 - this details what should be done around the eaves (ventilation) etc. Another place to visit is the National Insulation Association and these guys can give advice.