scottishjohn

thanks for the replies

what cleaning products and soap powders are ok with a treament plant so as not to kill the bacteria anybody that has used for for some time --what are you using ?

you only show one baton far better to use cross batons ,then there is no ledge for moisture or crap to build up on over the years single batons with osb sheeting caused my house to rot as all winter the dust etc were damp ,,so 25 years on i had a problem on the north side of the roof the extra cost of double batons is very small and also gives you a bigger gap

or below them change the Pb for insulated PB and loose maybe 35mm in head room,and you got a warm roof as it already has insulation above and only rafters are not insulated,but to be fair wood is a pretty good insulator

It is not really a cold roof that is where all the occupied space is insulated from all of the loft and roof --eg flat ceilings I am guessing as it has pB then it is occupieed below the insulated roof section I would call that a wram roof so back to your question I do not see any need to slit it as there will always be low pressure on one side of the house due to winds ,heating of roof etc etc so it should cause enough of a draft to pull from one side to the other,just make sure there are no cold bits where the eaves meets the walls

I may be being thick but why would you have ,as you say a gap if you have filled space between rafters with insulation ,the osb can be hard aghianst it both sides the eaves gap is to vent the cavity walls to exterior ? I am confused is this a cold or a warm roof system a drawing please

so basically a warm roof as if it was sips panels so there should be little or no moisture inside it and making holes wil surely induce a warm flow of air where moisture can condense from heat inside house If i understand you correctly ? like it has vaulted ceilings as in a room like a loft which is heated from house?

what is a cassette roof

vented dry ridge system ? then it can come out at the tiop which is where the heat generated between tiles and mebrane will wnat the air to go

If you make new stud walls just wrap the membrane around edges of panels before you fit them -then you have a complete seal ,by the time they are screwed together

If it was pointed both inside and out with cement mortar --not lime then there will be no or littlem ovement of moisture through a granite wall great if outside was lime pointed as it can go out that way , othherwise it can only move downwards through the wall to foundations and there will be no DPC in the walls thats the reason fro having ground level at outside lower than floor level - especially ona ahouse with no DPC

normal way to build modern houses is TF and sheeted on the back and vapour barrier on inside of insulation and a breathable barrier on outside of TF not really possible unless you going to build stud walls as panels and breathable membrane attached before panels are raised into place so you could do it that way if making new stud walls is your chioce

conversly putting it on the warm side between insulation and inhabited ppart would lessen the chance and as said before most moisture in the house comes from occupation and breathing asuming outer walls are dry as you said and with the air gap there which will be vented to eaves it should stay dry if cold as cold air holds less moisture

and not sure tape will stay adherred for next 50 years

I know some will say i,m making a bigger job than required youdo not need 150mm space behind studs 50mm +is fine and yes studs look very small you could replace them with larger ones and reduce space behind then fill with what ever your choice of insulation me i would go PIR jam them in the studs and fill any gaps with foam then your vapour barier on inside of insulation and if space and money allow insulated plaster board -- - foil backed pir will not absorb any moisture and will reflect cold back to the outer wall the most of the moisture will come from you living in there so thats why i say put it on inside of insulation and if done right there should be no cold spots to cause condensation attention around window reaveals is important - behind the uprights and under the lower internal widow ledge sealing it all this stage is the key so no cold spots to cause condensation you only spend once on insulation --and it pays back forever