How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

How is water getting into the outside walls of my home?

Wednesday, July 7, 2021

To better understand the ways that water can penetrate an exterior wall of your home, let’s start with the fact that water intrusion is not always liquid. It has three different states according to temperature, each with unique properties. The other two are solid (ice), or gas (water vapor). 

   Liquid water rolls downhill due to gravity, right? Yes, except where capillary action, the phenomena you see when a sponge sucks up water out of a puddle, comes into play. And, of course, wind-blown water in a storm can be pushed upward six inches or more into any unsealed opening in a home’s exterior, where capillary action sometimes takes it even further.

   Then there’s ice. Most materials shrink when frozen, but water expands. And it expands with tremendous force. This is the property that causes burst plumbing pipes during a hard winter freeze.

   And finally, there's water vapor. House-wrap material, which is applied over wall sheathing of a house under construction before the siding is applied. It is specifically designed to deal with the perplexing issue of water vapor movement through walls and it’s tendency to condense back to liquid form when it reaches a colder surface. Modern house-wrap allows water vapor to pass through, but not liquid water, because trapped water vapor that condenses inside a wall creates an insidious mess.

    Liquid water can enter a wall from the bottom, vertical surface, or top. A concrete foundation sitting in extremely wet ground or a high water table can suck moisture up into the base of a wall by capillary action if not sealed by plastic sheeting barrier below. Openings in the exterior surface of the wall allow driven rain or the spray from a misdirected sprinkler head into the wall. Even a small crack admits some water, a long crack is equivalent to a hole punched in the wall, and cracks typically open further after admitting water for a long period. A roof leak near the edge of the roof, especially under deteriorated flashing at the end of a valley, will drip into the top of the wall corner below.

    Humidity in outdoor air wants to migrate to the drier air inside your air-conditioned home in Florida. In physics it’s called seeking equilibrium. If you put any type of impermeable barrier on the inside surface of the wall—such as foil wallpaper—the moist air moving through the wall will condensate into liquid on the back surface, and eventually grow mold.

    We don’t deal with water’s solid form much here in Florida, other than uninsulated pipes bursting during a hard winter freeze, or freeze-cracking of some types of bricks if wet. But ice formation is a big problem up north.

    What can you do? Keep up with the caulking around windows, doors, faucets, light fixtures and other wall penetrations. Check regularly, and seal any cracks in the wall as they appear. Also, gutters with downspout extensions are great for avoiding rain splash-back onto walls and keeping puddling water away from the base of the house.

• • • • • • • • • • • • • • • • • • • • • • • • • • • •

    To learn more about water intrusion, go to some of our other blogs:

Why does my concrete floor slab sweat and get slippery? 

• What are the signs of stucco wall leaks? 

The inspector says that a missing kickout flashing caused water damage inside the wall. What's "kickout flashing"? 

Do stains on the ceiling mean the roof is leaking? 

What causes sweating (condensation) on the inside of windows in the winter? 

Where are the most common places to find wood rot on a house? 

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

Why is housewrap installed on exterior walls under the siding?

Why does condensation form on the outside of some windows and not others in the morning?

How can I prevent mold in my Florida winter home when I'm gone for the summer? 

• My bathroom is stinky and humid even though it has an exhaust fan. What can I do to fix it?

Should I buy a house that has hurricane flood damage? 

Should I buy a house with hurricane flood damage that has been repaired? 

Why do new homes have more moisture and mold problems than older houses?

What is the right humidity level in a mobile home?

Why are rubber washing machine hoses a safety risk? 

How do you test a shower pan for leaks?

Should I call a plumber or septic tank contractor when my septic tank backs up into the house? 

Why is old galvanized steel water pipe a problem for homebuyers?

What does polybutylene pipe look like? Why is it a problem?

Why is it a mistake to replace a roof and not replace its flashings?

What can I do to prevent roof leaks? 

What does freeze damaged brick look like? 

• Why is my roof leaking? 

• What are the signs of stucco wall leaks? 

Is it normal for a mobile home crawl space to be damp in Florida? 

• Why is my stucco cracking?

Water Heaters

Water Heater Age

"What Are The

Signs Of..."

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests



When It First

Became Code

"Should I Buy A..."

Park Model Homes


Shingle Roofs




Wind Mitigation

Roof and Attic

"Does A Home


Pool and Spa

"What Is The Difference Between..."




Concrete and

Concrete Block

Metal Roofs


Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants


Older and

Historic Houses

Crawl Spaces

Mobile-Manufactured Homes

Building Permits

Life Expectancy

Clay Soil





Exterior Walls

& Structures


Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers



Doors and Windows



Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps


Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.






Air Conditioner & Furnace Age/Size


Electrical Switches





Water Intrusion

Electrical - Old

and Obsolete


Foundation Certifications

Tiny Houses

About McGarry and Madsen



Buying a home in North/Central Florida? Check our price for a  team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.

Moisture Problems

Crawl Spaces