Why use membrane layers???

[christo4robin]

In roof and wall constructions, why use membrane layers?

It seems that schedules schedule volume, area, perimeter, etc. but not, say, amount of tyvek or ice&water shield.

That said, is there an advantage to using the membrane layers that I am missing?

[aaronrumple]

actually shows up as a line in the drawings....

[ejburrell67787]

And why must membranes have 0 thickness??

Is there a setting to allow substrates to have less than 5mm thickness?

A bit academic I know, but if we can draw / model to this level of precision, why not get it right?

I have a 2.5mm EPDM roof covering but have resorted to showing it as *Shock*Horror* 5mm thick!!

[PeterJ]

When I raised this point to Leonid Raiz in a round table discussion he queried why I would need to show that and suggested I look at my representation of elements. My particular bugbear that day was plasterboarded partitions with and without a skim finish and why I couldn't show a 3 mm skim.

The view that he seemed to be taking, the conversation moved on quickly, was that we should consider more where we need to show such things and then pehaps indicated them as drafted items if we do need that level of detail. I suppose it should make for faster models.

[trombe]

4Christo4,
bit off the subject, but I am curious to know how widely used Tyvek is.
With wind here for a start, non ruthless checking and repairing, can lead to the Tyvek crackling in a brick cavity wall, keeping the owner awake !!
Other issues aside, many have gone away from using it.
Breather type, bitumen soaked , kraft papers still used widely for walls as well as roofing planes.
Any comments ?
regards
trombe

[Henry D]

Trombe,

Interesting issue - so they use Kraft paper and felt vs. a poly vapor barrier and Tyvek in NZ? Tyvek and a poly vapor barrier is pretty much the standard around here. But I have clients who like to build "green" and they don't want to wrap their buildings in plastic so they want to use Kraft paper and felt. I would also be curious as to how they do it in the UK and other countries. Moisture, mold, breathability have become such big issues.

I have never heard of Tyvek flapping around in a brick cavity - if it's stapled properly. It will get ripped off a building when it's windy, but that is before the siding is applied.

[PeterJ]

Increasingly I find housebuilders, both private and commercial going over to Tyvek or similar products in place of a bitumen based felt at the roof plane.

We don't use any form of vapour membrane in the cavities in the work I do, but then it is largely masonry-cavity-masonry, you might want to ask the question of Rhys and Martin P, both active posters here, who do framed construction residential work.

[bclarch]

Tyvek is used regularly around here and I have never heard of it crackling in the wind once the masonry is up. I personally prefer asphalt impregnated felt. If you read the installation instructions for Tyvek they say that you are not supposed to leave it exposed to sunlight because of UV degradation. The allowed exposure time is ridiculously short (something like 6 days if I remember correctly). We all know that in the real world it is often left exposed for much longer than that. Typar is another version of a vapor retarder that has added UV resistance.

[christo4robin]

Interesting aspect of building in the Colorado Mountains - they like to use Ice & Water shield on everything - replaces other roof underlayments, also weather barriers on the wall.

[ita]

Sorry to want to change the topic back to the original issue - why membranes have to be 0mm in thickness?

The question is why have it at all if it is not going to be a part of the model? Question to Leonid, if that is the case as PeterJ states, why? There is no rationality to having the mention of the membrane in the dialogue box if it is not worth being part ofthe model.

In my office, we specify the the wall or roof sectionsystem as universal so there is no confusion, however I like to show an element (no matter what it is) on my drawings as a line. And . . . I don't want to have to draw a line on every detail when I can enter it once in the material composites for walls or slabs or roofs etc.

Further to this same topic . . . is it just me that cannot get this dialogue box to work first time? Why is it that when you choose a membrane layer and enter zero thickness the error message calls for a thickness. You then have to enter a value of 5mm or more to - change the dialog box. Then when you enter 5 (and it wont react to anything less!! ) - it then responds with a message that membrane layer cannot be greater than zero. Then and only then can you enter a zero and move back into the property box.

The process is a !@#@#$ waste of time!! Is it me or do others go through this process? If this is what the app does can we have it changed and the rationale behind membranes resolved?