What is the difference between a breather membrane and a vapour barrier

So as I explained earlier the 0. So, as I said, are comfortably under where they set the initial target. More impressively this air leakage result was achieved prior to installing our Procheck vapour control layer on the warm side of the insulation. Although the vapour control layer is not necessarily required as part of the air barrier system they may still be needed to control moisture ingress dependent on the precise specification of the construction. So we would always recommend an expert Hygro Thermal assessment be undertaken to verify this.

Building regulations compliance in the UK is assessed via the carbon emissions a building produces. So it allows characteristics for example air leakage rates, thermal insulation levels, areas of glazing or renewable energy sources like PV panels to be considered within the overall energy performance of that dwelling. In contrast by improving the air tightness of the dwelling the insulation thickness can actually remain unaffected.

So, if I can just try to summarize very quickly, and I understand has been a lot to take in during this webinar, essentially there is a ton of differences in the performance characteristics between the different types of membrane. All of these are very important aspects of the design process. Hopefully you can all hear me. I sit on a number of British Standards including the Control of Condensation and BS; the code of practice for roofing. We had a few questions submitted by email prior to the webinar starting and also a very interesting comment about kagools from Donald I think, so thank you for that.

One of the first questions that we had, Iain, was regarding the use of a membrane behind rainscreen cladding, or is it sufficient just to tape the joints with the breathable tape? However, the introduction of the vapour permeable Wraptite Tape has allowed for the taping of the insulation boards, purely just the joints, which has provided a lot of advantages without membranes hanging in the cavity, and potential fire risks. Especially over 18 meters the BRE have done some work with us to assess the fire risk of the Wraptite Tape used in this application over 18 meters with insulation boards and they have confirmed that they are comfortable with the use of the tape, purely the tape behind the rainscreen cladding in this application.

Another question we had was regarding the use of ventilation with air permeable membranes and obviously we covered that during the seminar but there was a question as to how you can prove that no ventilation is required with these types of membranes? So this question is related to the use of air permeable membranes within cold roofs without insulation. However, it still has some limitations on a vapour permeable membrane and what seems to have come out of this research is the benefits of air permeability along with vapour permeability.

A quick one here does Wraptite SA stick to block work? The Wraptite SA was obviously the external self-adhesive vapour barrier that I explained earlier in the webinar. Again another very good question with any adhesive, the substrate is very important.

Whether it be wet or dusty will affect the ability for any adhesive to adhere. So yes, it can stick to the masonry very effectively if the conditions are favourable. Jumping to a quick question about software. The Glazer method has been very successful for many years and the A Proctor Group have been able to provide condensation control calculations for a number of years using the Glazer method.

The A Proctor Group have invested heavily in the technology of WUFI modelling, where all our technical people can carry out WUFI calculations which significantly adds to the dynamic nature of the condensation calculation.

We can take into consideration the convection we can put in moisture sources, assuming that there is moisture within the existing building, rather than just assuming its new build.

Ok so typed question coming through from Clemont who would like it to be explained again whether there are actually effective airtight membranes which are also be vapour permeable that can be used in a breathing wall?

Ok, yes just for clarity what we are promoting here is a vapour permeable airtight membrane. Yet another very, very good question and one that we have lots of debates on, whether you need a vapour control layer with an airtight vapour permeable membrane. The straightforward answer, or less than straight forward answer is, it depends it on a number of factors in terms of the building wall fabric build-up.

The type of insulation is really important. Ok here we have a question from Mike. If you use Roofshield on the roof how does this affect air tightness? Roofshield is air permeable, so using Roofshield on the roof increases the air permeability of the loft space. The actual air tightness of the dwelling will depend on the surrounding area of the living space. So for air tightness of a dwelling we utilizing a cold roof the sealing is really important and there is many well seald ceilings now that are utilized to provide air tightness of the ceiling as well as the walls and that is in the living space.

Essentially, Mike, if your project was a warm roof you could use a product such as Wraptite SA or film laminate product which was airtight to complete that sort of air tightness. So, when used on an existing listed building and with Hydroscopic Insulation do you need to allow an air gap below the roof BPM and do you need to ventilate above if there is slate?

A lot of vapour permeable membranes require a vapour control layer to be used at ceiling level and that is really difficult in refurbishment projects. If you could type that, that would be great. Depending on the building envelope you can utilize the Wraptite SA internally or indeed if it was in the external insulation you could use it externally prior to putting on the insulation in an external wall system.

So,there are two threads to this question. So this is laid to a rough concrete floor sealing the membrane, cables and pipes and using an internal airtight membrane like Procheck.

So care would have to be taken sealing the wall and floor junctions. Our Wraptite has been used successfully in that area for draught-proofing on timber floors and they can be used on concrete floor so the junction between the wall and the floor would need to be looked at. If you had a detail of that we would more than happy to a look at that and going into that in a bit more detail. Is that correct? Cellulous fibre can be viewed as moisture tolerant and there has been some very good examples of cellulose fibre used as the insulation and the potential condensation risk and potential moisture management that the cellulose fibre provides, so in that case it might not be as critical to use a vapour control layer because you have a complete breathing insulation that is very effective.

Ok another question from Donald. As dwellings strive for more air tightness then that connection can be more complicated and therefore if air tightness is looked for we have obviously the Wraptite Tape BBA for walls. If you are then to put insulation on the top of that was all of low permeability then you are inhibiting the benefit of the Wraptite in terms of its breathability.

But utilizing the insulation on the outside the condensation risk would be driven outside the building envelope and many people in the cladding industry are utilizing Wraptite on the sheathing board and then applying the insulation on top of that.

So here they get two of the three benefits, water tightness, air tightness but not so much the vapour tightness. But because of the insulation on the outside the condensation risk is taken outside the building envelope and therefore a good application.

The job of a vapour control layer, or VCL, reduces the water vapour transfer through any building and reduces the risk of condensation forming. This is done by installing it on the inner side of the insulation — for example, in a pitched roof this would sit beneath the layer of insulation that has been installed between the rafters. It is essential that the VCL is continuous and sealed at all laps in order for it to perform correctly. While often also a membrane — in the form of a polythene sheeting — VCLs can come in a number of other forms.

For example, the Kingspan Kooltherm K Insulated Plasterboard contains an integral VCL, which allows for an increased thermal efficiency — helping you reach those U-values! To summarise, there are two important differences between a breather membrane and a vapour control layer:. However, both products — so long as they are properly installed and sealed — help to minimise the risk of condensation and, in turn, any damage to your home.

Breathable membrane for unventilated pitched roofs and timber frame walls. Insulated plasterboard which can be both bonded and mechanically fixed. Click here to find a stockist near you.

Uncover the facts: Vapour Permeable is the right choice behind both brick veneer and lightweight cladding. Figure 1: The drying performance of membranes Drying performance of membranes experiment notes: 1. The solution is Enviroseal ProctorWrap Enviroseal vapour permeable products allow water vapour molecules to easily pass through the film, but prevent the entry of liquid water.

Improves on-site work flow efficiency by allowing internal trades to commence work before the external cladding is applied. Improves air tightness which in turn improves energy efficiency, but still allows vapour to escape without condensing on the inside of the building frame. Protects the interior of the building from moisture and dust entry from the outside environment. If in doubt choose vapour permeable As condensation risk is difficult to predict and the consequences of condensation are not easy to manage after construction is completed, selecting a vapour permeable product is the recommended default solution.

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