Thatching Specifications
(Page Copyright of Mark Taggart)
Specifications - New build
In order to combat our humid climate I recommend the
following specifications for a New Build Thatched Roof.
Micro porous boarding to allow the Thatch to breath,
using felts and foils which act as vapour barriers, may interfere with the
movement of moisture through the roof structure ie interstitial condensation,
there is a belief that the actual dew point may occur with in the heart of the
Thatch.
A micro porous boarding which meets the Dorset Model is,
Gyproc Multi board/Glasroc counter
battened . See Fire Barriers page
One important note, you should not have to use any fire
retardants using this method as the Thatch is seen as Sacrificial. Fire
retardants which are sprayed on at 120 to 160 PSI , state that Rigging should
be viewed with concern over three years of age and they do not recommend
spraying Rigging over five years
of age.
Thatch min 300mm thick in one layer, beware of two 150mm
layers, "yes I have seen that Mr Ripley".
The pitch of the roof should be greater than 45 degrees.
2 by 1 battens counter battened, vertical battens follow
rafters beneath Multi board. Horizontal battens, first batten 125mm from face
of wall/wallplate and 225mm centers there after. I would use this method of
counter battening even with the screwed on method due to the need to fix back
into the rafters every second course, there by putting every second course
under the levering force created by the top batten.
It is important only to use reed whos quality meets the
recommend Nitrate content and that that reed is not fine. The reed must be of
a large bore to allow it to dry out quickly, fine reed although lovely to
thatch with and looks great when first thatched does not stand up to our
climate.
This is where we teach the English.
Blue stone can be found at any large farm/agricultural merchants . You
can spray it on when the job is complete and it will have the side effect of
turning the Thatch a blinding golden colour.
Be careful not to go mad with the mix as it will turn the Thatch a
bluey green, if applied in a strong dosage.
I have no doubt that Blue Stone fights bacteria and
prolongs the life of a roof in Ireland, the only Thatchers who dispute this,
are Thatchers from abroad who ignore the unique heritage and knowledge of the
indigenous thatchers of old in preference
to their training and knowledge from a different climate.
If you wish to do the 100% job you could dip the bundles
of reed in a bath of the solution, this is the historically correct way.
Beware of staining the building with Blue stone.
See CuSO4
With Water reed it is common practise to put a block cut
rigging on, this is for three reasons, it is highly decorative and due to the
reed being so tough it is not effected by the constant drips when raining
where the Rigging meets the coatwork. A flush or Traditional Rigging of Straw,
tends to open up when you put the Scallops into the Rigging ie it leaves
visual holes in the flush ridge, due to the reed being so tough and unable to
soak up the scallop like the straw does.
Best quality Straw for Rigging. Due to the fact that the
fixings/Scallops which initially hold the Rigging on will rot out in five
years, you will find that the straw has matted, put this with the galvanised
wire and you have rigging which will look after it self for another five
years.
Other details such as wind wall / skew details as well as
material Nitrate content, Easen details and Rigging design, contact Mark and
remember fit smoke alarms, I bought one for £9.99 and it must be a dual
purpose one, because it also tells me when my dinner is ready.
As a foot note, the ultimate specification would be to
build a Scraw roof on a derelict
traditional stone building and yes you will be called a lunatic for not
tossing this Historic structure, due to the savings in VAT that you will get
by building from a new. In the past I have built replicas, but they were not
authentic in my mind. Until such times as people can source bog oak and Scraws
from areas of land where grass runs into bog, this specification will remain
the Holy Grail of an authentic Irish Thatched home.
I still maintain that the Scraw roof was the first fire
barrier ever developed and would make the statement that they would have been
found in Celtic round houses where the only chimney was a hole in the roof,
with no means of controlling sparks from a fire. This would explain where the
Scraw roof came from, as it is easier to tie the thatch directly on to the wooden structure, may that be from using
deer hide or straw made into rope . If you
think I am wrong, then why would a Celt go from tying his Thatch on a Celtic
round house, to deciding to go out and dig 50mm thick sods from his front lawn
and put that on his rectangular pitched roof before he thatched it, so stick
that in your pipe and smoke it Time Team. As for all those replica Celtic
round houses built with out the Scraw, consult Celts in the future or as most
Archaeologists like to call us in England “The Ancient Britons”.
As for the traditional stone walls, I heard a theory not
so long a go that these stone walls contain the same carbon/silicon properties
found in recording tapes. The theory went on to say that during the right
atmospheric conditions these walls can literally tape conversations of the
occupants and at a later date play them back under different conditions. It
was a theory to explain the things that go bump in the night , but I think its
just another reason why people should preserve these homes whos walls have
ears and stories to tell.
Building
Control Web Site
www.thatchireland.co.uk