Building Envelope

by | Mar 9, 2021 | Renovations

The Importance Of Your Building Envelope

What is a “building envelope” and why is it so important to your home? A building envelope typically consists of some type of construction paper. Examples of these include tar paper, tyvek, typar or homeguard.

Tar paper is commonly called “building paper” whilst Tyvek, typar and homeguard are called “house wraps”. The building envelopes functions include protecting the building’s sheathing from water, acting as a wind barrier, and in some cases a vapour barrier.

Which is better house wrap or building paper?

When you are renovating the exterior of your home and are wondering which is the better product to use beneath your cladding. There are many different products to choose from and in a variety of price ranges, so picking one can be quite daunting.

Whether you’re doing the renovation yourself or hiring a contractor it is important to equip yourself with the knowledge of what the product design and function is before it is behind your siding!

Building paper pros and cons

Tar paper falls under the category of “building paper”. It’s basically tar paper felt. It comes in several “grades” 10- minute, 20-minute, 30 minute, and 60 -minute. The “grading system” is based upon the amount of time it takes for a moisture-sensitive chemical indicator to change colour when a small sample is floated in water.

Typically, in BC where tar paper is selected, a double layer of 30-minute is used. Tar paper acts as a water repellant layer as well as a windproofing layer beneath your cladding. It has been around for hundreds of years and is still effectively used to this day.

However, like most things it does need to be installed correctly. Proper overlap and checking tears are a must. All too often I have peeled back siding to discover minimal to no overlap or massive tears that were covered up. I have also seen the product disintegrate due to constant exposure to moisture causing rot to the building.

I have heard many people complain that tar paper is difficult to install…and on a windy day, I would agree with them. but for the most part, it’s quite easy to handle. It comes in a 3-foot roll and only weighs around 10 pounds.


  • UV resistant (will not deteriorate when exposed to sunlight)
  • Cost-effective (cheaper than housewraps)
  • Long-lasting (when installed correctly)
  • Easy install (if not too gusty)


  • Lots of seams
  • Not a vapor barrier
  • Does not allow the house to breathe as well as housewrap

Housewrap pros and cons

The two most common types of housewrap are typically Tyvek or Typar. These envelopes are designed to keep air and water out, while allowing water vapor to escape. Installing any of these two products on your house can help reduce energy bills as well as helping keep your home cooler in the summer.

When installed correctly this is a wonderful product to use especially when you are renovating your house. You will notice a difference. There are downsides to this product though as well. It is more costly than tar paper. When exposed to sunlight for an extended period it begins to deteriorate.

For Tyvek, you have about 3 months of exposure before the product’s air and water protective properties are negated. Typar gives you up to 6 months exposure but after that, it too will begin to deteriorate.

I have seen it time and time again homeowners installing a housewrap on a shed, garage or addition on their home and just leaving the product up for years thinking that it is protecting the sheathing on their building when it is not. So, if you are going to choose a housewrap be sure to cover it with exterior cladding before the UV destroys your investment.


  • Allow home to “breathe”
  • Vapour barrier


  • Vulnerable to UV light
  • More costly than tar paper
  • Requires more time to install


I have used both tar paper and housewraps over the years and both work great at protecting your sheathing…when installed correctly. I find Typar to be the product I go to more on renovations, however.

It is marginally cheaper than Tyvek and easier to work with. Tar paper is great at protecting against wind and rain but traps water vapour against the sheathing.

Why to change your envelope when renovating your exterior?

I often tell homeowners that the “leaky condo” fiasco that happened in BC was one of the best things that could have happened to homebuilding in BC. It revolutionized the way we waterproof our buildings and produced one of the best building codes in North America.

Two of the biggest problems I find when I renovate a home is the “negative laps” on the envelope or no paper at all! Paper is installed typically from bottom up. Ensuring that each layer overlaps the other. Like scales of armour. Water follows the laws of gravity and runs down.

A “negative lap” occurs when the installer overlaps the paper in a way that creates an open seam. The moisture then runs down behind the paper saturating the sheathing causing rot.

I approached an installer one time on a new construction build, I noticed that he was installing cedar shake and vinyl siding right over the top of the OSB sheathing on a detached garage. I asked him why he was not papering before installing his cladding. He responded confidently “because nobody lives in the garage, you only have to paper a dwelling”.

The sad part is it’s not an isolated incident. On homes built in the 70’s to early 90’s, I have found it quite common to find the gables not having paper on them. That is why I stress it to the homeowners to remove their old cladding on their home and re-envelope rather than side over top(this can be done over stucco but I advise against it).

The exterior cladding of your home needs regular maintenance and does not last forever. Many people wonder how long does siding last, and is their home ready for an exterior renovation. If your home is more than 20 years old, then it is a good idea to have an experienced exterior contractor inspect it to help prevent structural damage of your siding and building envelope is leaking.

By upgrading your building envelope, you not only ensure that it is installed correctly it can also help get the full R rating for your insulation saving you money in the long run.

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