How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes

Why is housewrap installed on exterior walls under the siding?

Saturday, September 22, 2018

Siding applied over a wood stud frame house structure is water-resistant but not waterproof. It doesn’t matter whether its wood, vinyl, or fiber-cement siding, brick, or stone: water will occasionally get behind it. Also, exterior siding materials do not provide an effective seal against air leakage through the wall.

   Modern housewrap—the white plastic sheeting with repetitive company logos stamped across the surface—is a barrier sheet that has the special ability to resist liquid water penetration but allow water vapor to pass through. This allows moisture to escape from the inside of the home, instead of condensing on the interior of the wall assembly and possibly causing mold growth. At the same time it prevents air movement through the wall when properly installed and taped, which adds insulation value to the wall.    The most popular housewrap brand is Tyvek, manufactured by DuPont from flash-spun, high-density polyethylene fibers; but black roofing felt, also called tar paper, was the original housewrap and continues to be used by some builders. 

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To learn more about exterior walls and structures, see these other blog posts:

What is the average lifespan of a house foundation?

What causes vertical cracks in fiber cement siding planks?

What causes raised white lines of residue on a block wall that are crusty and crumbling? 

What is the difference between soil subsidence, heave, creep, and settlement? 

How much ventilation is required for the under-floor crawl space of a home? 

 What causes stair-step cracks in a block or brick wall?

What causes a horizontal crack in a block or brick wall? 

How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

What causes the surface of old bricks to erode away into sandy powder? 

What are the pros and cons of concrete block versus wood frame construction?

Should I buy a house with a crawl space? 

Why is my stucco cracking?

There's cracks running along the home's concrete tie beam. What's wrong? 

What would cause long horizontal lines of brick mortar to fall out?

How do I recognize serious structural problems in a house?

What is engineered wood siding?

Should I buy a house that has had foundation repair? 

What is a "continuous load path”?

Should I buy a house with asbestos siding?   

How can I tell if cracks in the garage floor are a problem or not? 

What do you look for when inspecting vinyl siding?

How do I recognize serious structural problems in a house?

Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

Should I buy a house with structural problems? 

What are those powdery white areas on my brick walls?

What causes cracks in the walls and floors of a house?

How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

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