Cavity Trays discusses partial fill insulation
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partial fill insulation
Cavity Trays states that when constructing cavity walls incorporating partial fill insulation, the insulation terminates at plate level.
It is common practice to also terminate insulation at plate level across the gable ends rather than extend it up to the roofline.
Cavity Trays poses the question of whether the top of the insulation where it horizontally crosses each gable end should be protected against water ingress given the expanse of unfilled cavity wall rising above it? Could penetrating water use the top of the partial fill insulation as a bridge towards the inner skin? Rainwater penetrating an exterior skin of a correctly constructed cavity wall should not get anywhere near the insulation; in practice this is not the case.
Within the triangle of masonry forming the gable are a large number of wall ties.
Water will track along a perfectly positioned wall tie until the twist or feature of the tie directs the water to drip off it and fall into the cavity below.
Within a 100mm cavity incorporating 50mm partial fill insulation, a conventional tie can discharge water halfway across the cavity.
Where that partial fill insulation terminates horizontally across a gable, the top of it is exposed.
Water falling onto an exposed insulation top edge will either pool on it or it will gravitate into it.
In both instances with the insulation secured against the inner skin, capillary permeation results.
This can occur where tie and insulation placement is perfect - the problem where ties are not perfectly centred or insulation placement is uneven is more extreme.
Best Practice is to protect the top of the insulation to prevent this possibility happening.
Using a preformed cavitray will ensure any water dripping from higher level ties cannot fall onto or into the top of the insulation.
Cavity Trays manufactures several trays suitable for this purpose.
A popular choice of contractors is the Type CD Cavity Dropcloak.
This preformed tray conveniently does not require building into the exterior skin but importantly protects the insulation top and the inner skin.
The Type CD Cavity Dropcloak is listed within the Technical Manual ’Protecting the Building Envelope’, released by Cavity Trays.
Type BA Cavity Barrier Arch cavitrays from Cavity Trays have been designed for use in shaped rather than horizontal cavity walls to provide opening protection. Type BA cavitrays offer total protection to the angled head, extending upwardly and outwardly to prevent the build up of concentrated water wash.
New Pyramid Weep for cavity masonry download
The new Pyramid Weep for cavity masonry from Cavity Trays replaces traditional reed straw systems. Triangular in profile, the new weep provides an aesthetically neutral means of removing water that may permeate a structure. The possible flow width of the weep is maximised due to its flat base which also allows it to bed as flat and low as possible to service water evacuation from lintels, dpc’s and trays. The Pyramid Weep is manufactured using PVCu and, as a result, will not rot.
Cavity Trays is reporting that cavity walls that support an opening using separate lintels will improve the overall thermal performance of the structural opening as the lintels do not connect and therefore do not conduct heat loss. Using this method alongside a self-supporting Cavitray and an infilling profile Cavistock enhances performances levels even further. This arrangement can promote a lintel value of up to 0.05W/mk.
Cavity Trays movement challenges the lastest British Standard PD 6697: 2010 detail that results in the entire parapet masonry above the DPC being separated from the masonry below the DPC and is not the ideal structural arrangement for a highly exposed wall at the top of a building. They outline why the use of preformed self-supporting Type P parapet cavitray is the preferred option.
Cavity Trays, already the only UK manufacturer of preformed cavitrays to hold European Technical Approval, has now secured additional approvals from LABC Registered Details (Local Authority Building Control) for preformed curved and straight cavitrays plus its extensive range of Cavicloaks.