Condensation on roof nails in attic

Inspect the Attic or Roof Cavity for Signs of an Ice Dam Leaks, Under-roof Condensation or Moisture Problem

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How to inspect an attic for condensation, leaks, or moisture problems:

This article describes inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems, in buildings. It describes proper roof ventilation placement, amounts, and other details.

This chapter "How to Inspect in the Attic or Roof Cavity for Signs of an Under-roof Condensation Problem, is part of our article series on "Attic Condensation".

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Inspecting in the Attic or Roof Cavity for Signs of an Under-roof Condensation Problem

Blocked soffit on a 1920's home means no air intake path (C) Daniel FriedmanHow to inspect a building attic for evidence of ice dam leaks, condensation, frost, or moisture. How to detect roof venting deficiencies, attic insulation defects, and attic condensation problems.

Check the Entry & Exit Pathways for Attic Ventilation Air

After examining the eaves or lower roof edges, look up at the ridge for a continuous opening on either side of the ridge board, providing an exit vent path.

On some buildings I've found that a ridge vent was installed but the installer just nailed it over the existing roof sheathing, forgetting to cut the necessary opening.

"Spot vents" on lower roof slopes, or power vent fans are not as good a substitute for the year-round passive venting provided by a ridge vent.

Our photo (left) illustrates a common construction practice on wood framed homes built in North America into the 1950's: at the house eaves blocking was nailed between or against the ceiling joist ends to minimize air flow into the attic at the house eaves or soffits.

You can see dark mold stains on the underside of areas of this roof.

The presence of perforated panels covering the soffit undersides on this home amounted to faux-venting since there was actually no air pathway into the attic.

Check for Signs of Attic Condensation & Moisture

Frost in attic over a log home (C) D Friedman A Puentes

Inspecting attic spaces in winter weather in freezing climates you may find extensive frost over roof sheathing and framing, as shown in home inspector Arlene Puentes' [2]photograph of a log home inspection (at left).

Even in warm or dry weather you often will see stains around roofing nails penetrating the roof sheathing, or condensate drip spots on the attic flooring or insulation (Left photo below).

This is caused by moisture condensing on the roofing nails and dropping to the surface below. This is sure evidence of a condensation problem. The pattern of drip marks may be remarkably just like the pattern of roof shingle nails which protrude through the roof sheathing.

Winter condensation on the nails, even forming frost in freezing weather, rusts the nails and stains the roof sheathing around them.

Frost later melts off of these nails and drips onto the floor below.

The pattern may occur more on the cooler or north slope of the roof.

attic drip spots from attic condensation

If attic stains are from roof leaks, (photo above) they will usually be much larger and will appear on the sides of rafters, on larger areas of the roof sheathing, and on larger areas of the attic floor.

If you see evidence of extensive roof leaks or condensation leaks, I'd also check the insulation and the attic side of the ceiling drywall for a hidden mold problem.

attic stains from roof leaks

If you see condensation drip stains in the attic  photo above), you'll be confirming what you suspected from outside -- inadequate ventilation.

attic stains from ice dams at eaves

Be careful and don't overlook viewing the roof eaves.

There could be rotting fascia boards, decaying rafter ends, and delaminating plywood.

Look in that location for moisture-stained roof sheathing, and look carefully for ice dam leak stains into the eaves, such as the water marks shown in this photograph.

How to Inspect the Attic for Moisture - Stains Around Roofing Nails

Attic shows roof nails protruding

Rust or stains around roofing nails that protrude through the attic sheathing (they're supposed to stick through) are a clear indication of high attic moisture.

Our photograph above shows roofing nails protruding through plywood roof sheathing visible in an attic where there is no under-roof condensation or moisture problem.

Attic shows condensation stains at roofing nails

Our photograph above shows roofing nails which have rusted and stained the roof plywood in an attic where indoor moisture has risen through the building to condense on the under-side of the roof.

Attic condensation stains

Our photo at left shows the typical staining pattern in an attic where there has been modest condensation at the roofing nails.

If you perform this inspection step in winter in a freezing climate you may find frost on these nails. In other seasons or in non-freezing climates you will see rust on the roofing nails and often stains on the roof sheathing surrounding the nail.

On an older home that has been re-roofed, you may see these nail-stains but no nails - the old nails may have been removed during re-roofing, leaving just the rust-marked roof sheathing.

Excessive attic moisture condenses on the cool metal surface of the roofing nails, causing corrosion or rust on the nails and stains on the surrounding wood materials.

These same condensation points - the roofing nails - will often map exactly the drip stains found on the attic insulation or attic floor below each nail.

Because moisture may enter the attic more at some locations than others, for example over a bathroom or kitchen, nail staining and drip marks will not be uniformly distributed throughout an attic.

How to Spot Attic Mold Due to High Attic Moisture or Roof Leaks

Photo of brown mold in an atticPenicillium mold in an attic

These photos show mold on attic surfaces due to high moisture in that area. While many inspectors notice dark mold or mold-suspect material on roof framing or roof sheathing, it is at least as important, and often more important to spot the light-colored molds that may also be present - often these are the more hazardous, particularly if building conditions cause air movement downwards out of the attic into the living space or into an attic-located HVAC duct system.

The brown/black attic mold on plywood in the left-hand photo is easy to spot and is often an allergen or problematic attic fungus like Cladosporium sp., Pithomyces chartarum, Ulocladium sp., or Aureobasidium pullulans but the light colored mold on the tongue-and-groove pine roof sheathing in the right photo was found to be Penicillium sp. which is more likely to be airborne and transmitted in the building.

How to Correct High Attic Moisture, Condensation, Leaks

A first step in fixing a wet or moist attic problem is the correct identification of the source of the moisture.

Stains or even wet areas on the under-side of roof decking and on rafters can appear to be a roof leak but in fact moisture may be entering the attic not from above (outside and through the roof), but by rising through a building suffering from leaks, a prior fire extinguishment, or most common, a wet basement or crawl space.

Home inspector David Grudzinski[1]provided the attic moisture photographs shown below.

Photo of brown mold in an atticPenicillium mold in an attic

From just the photographs, and without having inspected the building exterior, roof, nor other areas, the photos look like a roof that had numerous leaks, perhaps from worn out roofing, possibly even some rotting sheathing.

The photos show areas of apparent mold on some rafters.

But especially in the 2nd photo at above right, the very extensive condensation stains around the nail protrusions through the roof deck tell us that the whole attic interior has been soaking wet. Now for the big question: is this wet attic caused by roof leakage or is there a building water entry problem?

Mr. Grudzinski provided the additional, crucial diagnostic information about this wet attic:

The basement was a wet one, and as is typical the moisture finds a way to the attic. This house had poor insulation, and a poorly insulated attic access, as well as a whole house fan which are notorious for heat loss causing condensation. The person buying the house is a pregnant female and I strongly advised complete and thorough mold testing and remediation.

In other words, an expert roof and attic inspection include an inspection of the entire building, basement to roof, in order to understand where moisture or condensation are originating and what may have been their effects on the building.

A Wet Attic Risks Hidden Mold Contamination of its Insulation

Also, we wonder if, in a soaked area like this where fiberglass insulation is present, because of the risk of hidden mold in the insulation (see FIBERGLASS INSULATION MOLD) it may be worth checking the attic side of the ceiling drywall below the areas of most-apparent-worst leakage into that space - looking for water stains there, mold, &c.

If you find significant levels or large areas of mold in your attic the mold should be cleaned - that is, removed. Do not rely on magic bullets like sprays alone. The spray approach does not remove the problem mold and it may spread it into otherwise uncontaminated materials like insulation.

Don't tear off the roof over a moldy attic: Unless the mold-causing conditions have also rotted framing or delaminated plywood roof sheathing, structural removal/replacement, such as a roof tear-off are unnecessary and inappropriate. But don't forget that if you see attic mold the insulation or ceiling drywall below may also be moldy.

See HOW TO FIND, TEST FOR, & REMOVE MOLD IN ATTICS for details about where and how to look for attic mold and what to do about it.


Continue reading at ATTIC VENTILATION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.






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ATTIC MOISTURE or MOLD at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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Frequently Asked Questions (FAQs)

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Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.

Question: diagnosing moisture high on building walls

I have a double wide manufactured home that I'm renovated. It has vinyl siding and perforated soffits common on manufactured homes. We've noticed moisture high in the walls all around the home and can't identify the cause. Any ideas? - T.B., Colorado


What T.B. found was a combination of accumulated snow or frost or ice in the home's eaves, possibly due to wind-washed insulation, moisture and condensation, or snow and ice building up in the eaves, combined with leaks into the house walls when weather warmed and the accumulated snow or ice melted. Details about this Q&A are at MOBILE HOMES, DOUBLEWIDES, TRAILERS.


(Feb 14, 2014) Ben Bailey said:
Some of my roof decking boards have holes in them from previous leak damage. there is 4 spots across the whole roof. is there a way to fix or resecure this in an acceptable way without tearing off the roof?


Ben, are we fixing the roof deck or the leaks? Most likely the leaks must be addressed first. Then if the area of damaged decking is just a few inches it's probably ok to leave it alone until further evaluate at re roof time. If there are large areas of decking rot it may be impossible to repair leaks without re-decking the damaged areas. The decision to make spot repairs vs complete reroofing depends on the overall roof condition and it's estimated remaining life.


(Aug 11, 2014) Anonymous said:
Do I need to encapsulate moldy delaminated decking before removal ? It HAS to come off in several areas. I heard the mold could spread when agitated.
I have suspicions of the origins of leakage & am going to correct anything I can.Cant go another winter the decking is 100% saturation



Typically demolition of damaged roof decking is performed from outdoors - from the rooftop, not from inside.

If there has been a history of leaks or high attic moisture you should be alert for contaminated insulation, upper side of ceiling drywall etc. If those conditions present there's more cleanup to do. If they are not, you might want to put down some tarps in the attic before the roof demolition.


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Technical Reviewers & References

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  • [1] David Grudzinski, Advantage Home Inspections, ASHI cert # 249089, HUD cert# H-145, is a professional home inspector who contributes on various topics including structural matters. Mr. Grudzinski, Cranston RI serving both Rhode Island and Eastern Connecticut can be reached at 401-935-6547 fax- 401-490-0607 or by email to Mr. Grudzinski is a regular contributor to - see DECK FLASHING LEAKS, ROT Case Study, and BASEMENT WATER MOLD IMPACT and VERMICULITE INSULATION for examples.
  • [2] Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at
  • "Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy
  • "Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy
  • "Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
  • "Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
  • "Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy
  • "Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
  • "Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
  • Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
  • Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.

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  • Carson, Dunlop & Associates Ltd., TorontoCarson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
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  • Home Reference Book - Carson Dunlop AssociatesThe Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.

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condensation on roof nails in attic
Roof, inside my attic the nails come through the roof boards. The nails have condensation on them?
Ensure there is adequate attic ventilation using any combination of gable/soffit/ridge vents.

Prolly a combination of
inadequate ventilation (even in the winter, ventilation is required),
a faulty/nonexistent vapor barrier to the conditioned living spaces and
insufficient insulation.

Frosty Roof Nails

Q: The last couple of times that I've been in my attic when the temperature is really cold, I've noticed ice on the nail tips sticking through the roof sheathing. Do you know why? Is there anything I should do about it?


The last couple of times that I've been in my attic when the temperature is really cold, I've noticed ice on the nail tips sticking through the roof sheathing. Do you know why? Is there anything I should do about it?

—Stasia Bremer, Wood-Ridge, N.J.


Tom Silva replies: What's happening is that warm, moist air from inside your house is seeping into the attic and the moisture is condensing and freezing on the cold steel. And yes, you should do something to stop the seepage because it can reduce the effectiveness of your insulation and encourage mold growth.

There are three steps to solving this problem. First, seal off any openings for air to leak into the attic. Maybe a bathroom fan isn't venting outside or the pull-down attic stairway needs weatherstripping or the light-fixture boxes aren't sealed. A home-energy specialist with a thermographic imaging device can pinpoint many small leaks you can't see.

Second, try reducing moisture levels in the house by turning on exhaust fans when bathing and vent fans when cooking.

Third, make sure the attic is well ventilated so that any moist air that gets past your defenses has a way to escape. Soffit and ridge vents are more effective ventilators than fans, and they don't use any energy. If you already have these vents, make sure they aren't being blocked by insulation.

Frost on Nails in Attic
frost on nails

This is frost on a piece of high quality insulated glass in my man cave. The outdoor temperature was minus 6 F and there's NO humidifier in this building! The same frost on nails could be happening in my attic! Copyright 2018 Tim Carter

Frost on nails in attic spaces may frighten you. It should to a degree. It's important to realize frost is in your attic for a few reasons.

Frost on Nails is Frozen Condensation

Remember the last hot and humid day you were sitting outside drinking a cold beer, iced tea, soda or glass of ice water? The outside of the can or glass had drops of water on it that rolled down and got the table wet.

Another key point is the water moments before was invisible. The water was a gas in the air surrounding you and the can or glass.  The water is the same thing that creates the uncomfortable humidity most people loathe.

This exact same process is happening in your attic during extreme cold weather. The nails that you see in your attic get as cold as the outdoor temperature. The air in the attic has water in it and it condenses on the cold metal.

A point often overlooked is that since it's winter, the water freezes on the cold nails. This is why you see the frost.

frost on nails

A tool like this shoots nails through shingles. The tips of the nails are supposed to penetrate through the wood on your roof. The nails are 0 F too as long as the roof is shaded. Copyright 2018 Tim Carter

Related Links

Turbine Whirlybirds Can STOP FROST

Frost in Attics - Mystery Revealed! and How to Eliminate It

Free & Fast Bids

CLICK HERE to get FREE & FAST BIDS from local roofers that can increase the amount of ventilation to STOP FROST.

How to STOP the Frost on Nails

At the present time, here's how to stop the frost you're seeing in your attic:

  • lower the humidity in the house
  • increase air flow through attic

It's not easy to lower the humidity in your home. Many sources advise you to ADD humidity to your indoor air to feel warmer in the winter.

It's easier to increase the air moving through your attic using roof turbine vents and other traditional roof vents.

It must be remembered you must have great soffit ventilation so the air travels through your attic as a constant breeze.

Without delay this air movement brings in drier outdoor air into the attic. The dry air evaporates the frost!

Old Houses Didn't Have Frost

A point often overlooked is old houses didn't have this frost on nails problem.

The houses were drafty and the humidity couldn't build up to cause a problem. Your modern house is much tighter and the humidity can soar.

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