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Monday, August 12, 2013

How To Install A Vapor Barrier In Your Crawl Space

Installing a vapor barrier in your crawl space can go a long way in protecting your home from moisture that can damage your subfloor.  Most homes have vapor barriers covering the soil under their houses, but surprisingly many do not.  If your home is one of them, pay attention and I will tell you step by step how it is done.  There is nothing scientific about laying down a vapor barrier.  It is really hard work and is not for the claustrophobic, but any motivated do-it-yourself person could get the job done.  Here is how...

What type of vapor barrier material is needed?

Many older homes have a vapor barrier in place, but are not up to code and may not be functioning the way they should.  The type of material that should be used is a 6 mil black plastic.  If your home is older, you might see a 4 mil plastic or plastic that is clear.  Both of these are not as effective and should be replaced.  Of course, going with a thicker mil is always going to be better, but the cost goes up substantially for anything over 6 mil.  There are many companies using a really high quality vapor barrier that is 20 mil, but this type of material costs thousands of dollars and I am not quite convinced it is worth the price.

Getting started

First, you need to clear the crawl space of debris and any remnants from older sections of vapor barrier.  It is not recommended to lay a new vapor barrier over an old one.  Vapor barrier is often called "Visqueen" which is just a brand name, but there are actually a few brands out there that you can use.  We generally use "Husky" brand which can be purchased from Home Depot.  They come in rolls of 1000 square feet or 2000 square feet, but you want to buy more than the actual square footage of your home because you will be overlapping a lot.  If your home is 1000 square feet, you are probably going to end up using about 1200 square feet of vapor barrier, so plan accordingly.

Installing the vapor barrier

Look for the path of least resistance to roll out the vapor barrier.  Find the longest, widest run between the posts under your home to unroll it.  It is easier to start from the back and work your way towards your crawl space entry.

Cutting the vapor barrier

Like I said earlier, you are going to want to overlap it.  You should have about one foot of plastic overlap the foundation wall and about one foot overlapping the seams of the plastic.  The trickiest part of installing the vapor barrier are all the posts in the way.  When you unfold the plastic, take a sharp box knife and cut flaps to lay on either side of the posts.  It is okay if there is little gaps around the posts. 

Smooth it all out

Once you have it laid out and the flaps between the posts cut, you need to start crawling around and smoothing things out a bit.  Remember to keep about a one foot overlap on the seams and the foundation and realize that some gaps are okay.  A rule of thumb is that at least 95% of the ground must be covered.  

A couple things not to do

Many people ask about taping all of the seams.  This is a lot of extra work and can be useful, but we do not recommend it.  We prefer a floating vapor barrier so that water can drain if a pipe ever bursts or if water gets on top of the vapor barrier.  Think about it, if water cannot drain off the top of the vapor barrier, it is counterproductive to even have one!  

If you think you want to try doing this on your own, you certainly could do it.  Just be prepared for some hard work.  If you are in the Portland, Oregon or Vancouver, Washington area and need some help with it, be sure to give us a call.  We can give you a free estimate or at the very least, we can give you some advice.

1 comment:

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