Colm O HAonghusa
USB as a vapour barrier Interesting thread this thus far. I work with German made wood-fibre products here in Ireland and the general consensus now is that OSB, even 18 mm ( almost 3/4") thick graded as exposure class 1 cannot be relied on as a reliable vapour barrier. Tests have shown that even within the same batch there is a hugh variability in permeability levels. If the budget will take it then I use an intelligent membrane over the inner face of the OSB, else use a more normal VB. Unless the OSB is required for racking then 1/2' can be used which reduces the cost somewhat. In the case under review, the lack of ventilation in the cavity behind the brick facing did'nt help. What is not clear is if there were any fixings from the brick through the external sheathing to the timber frame.
Posted: 03:47 pm on June 2nd 2012
OSB and European external render systems The tests on the OSB to which I refer were to tape a a layer of a barrier on the inner face of the OSB and then apply the blower test with negative pressure. The layer bubbled as soon as there was a very small negative pressure. This to me is an air barrier failure. This would suggest that in the case under review, the lack of air resistance on the inner face, ie the OSB meant that the solar vapor pressure build up had somewhere to go, line of least resistance so to speak. The European renders on the external wood fibre materials, typically used in EWI projects, differ from a brick layer in so far as they dont have the mass or the specific heat capacity to heat up in such a concentrated way as brick. Neither do they aborb as much water in such a concentrated area. They are, by design, water resistant but vapour permeable and work well in tandem with the natural materials used as insulation. I cannot comment on the performance of foam/PU/PI/etc rigid insulation behind European type EWI renders. There is a lot of it being used in retro work for the housing stock in UK and Ireland but I think the jury is still out on the longer term performance issues I cannot comment on the paint issue and its role in the EWI buildup, in any projects I have done the colour is in the render and no further painting is required. However it does point to the need to tell the home owner that if painting, it needs to be chosen carefully. Micky mouse weep holes are never going to perform. Just consider the code requirements for ventilated eaves...
Posted: 07:15 am on June 3rd 2012
Greetings from Dublin An article (which is linked below) on what to look for when 'specifying' LEDs was discussed at a recent CIBSE/ASHRAE symposium in Dublin. I hope it will help http://arrow.dit.ie/sdar/vol1/iss3/2
Posted: 08:07 am on April 20th 2014
Larsen Truss question for Andrew Michler if I may please Andrew, Greetings from Ireland. Can you describe the makeup of the 14" Larsen trusses please, including the depth of the rebate or dado to take the web. I have not come across it before and it may just solve a problem I have for increasing the depth of loose fill cellulose. I am familiar with "I" beams, joists but they are way too expensive for what I need. Thanks. Colm
Posted: 04:32 pm on October 15th 2014