Couple of other points.
People assume that modern treatments and details can be transposed into older constructions.
Where these involve reducing the breathability of the construction, they can cause problems.
Typical errors can include cement rendering over old brickwork filled with lime mortar. Cement render does not breathe like lime based products and will seal moisture into the construction leading to other damp problems, when all that may have been necessary to restore weathering ability was to rake out and re-point the brickwork.
Regarding the roof, tightly fitting felt under perfectly flush slate layers can reduce ventilation, leading to problems for wall plates and roof timbers going forward.
That having been said, roofs with no felt and/or inadequate valley boarding and lining can allow meltwater from our once-every-ten-years deep snowfall find its way into the attic space.
Its not uncommon to find lime mortar reinforced with animal hair behind the slating in the attic - this traditional method of sealing can also reduce ventilation.
When considering roof repair, give some thought to
- increasing the width of the valley gutter
- improving the "steps" in the covering to deal with both the issue of meltwater and reduce the likelihood of blockage,
- widen the gutter to provide safer working space for roof maintenance.
People assume that modern materials are suitable for remedial works, particularly slates and tiles.
Where the weight, size, gauge lap and pitch are not a match for the original you can end up with; -
- too great a weight of slate for the rafters or
- too little lap for the detail to work correctly
If measures are taken to improve weathertightness which reduce breathability then additional vents should be considered.
Finally before you undertake any remedial work you should take advice from a building professional experienced or qualified in dealing with period houses.
FWIW
ONQ.
