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Question DetailsAsked on 3/23/2018

I am building a home.I can see daylight between my sheathing and siding in my attic .what should I do.?

It is not the soffit or roof vent. It is the side wall.Is it missing tyvek?

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OK - If you are looking from inside the house at not yet drywalled, uninsulated exterior walls and seeing daylight through the joints in the sheathing (coming through siding then through the sheathing expansion gaps), then yes - they forgot the water barrier/housewrap, assuming what you are seeing is not daylight coming through a semi-translucent housewrap. If windows or doors are not installed or not flashed out yet you should be able to see the housewrap/water barrier at those openings.

Otherwise, do you mean the eaves - the gap between the rafters (or top chord of roof supporting trusses) over the top of the exterior wall, or a gap between the siding and the wall framing sheathing in the exterior wall ? Images of both below:

If the eave opening as shown above where daylight is showing over the baffles (you may or may not have them) used to keep the insulation from blocking the eaves, with a normal roof with an attic which is not within the "conditioned space" - so open to outside air, not heated or air conditioned, you need airflow to remove moisture (either making its way up from the house, coming in with outside air and condensing or frosting up in the attic on cold nights, or from roof leaks) and heat from the attic - free flow of ventilation from the eaves to ridge or gable vent or roof vents, and the eaves have to be open to provide this airflow. General rule of thumb is the open eave (and exit) vent space should be not less than 1/300 the square footage of the roof itself, distributed across all eave rafter "bays". 1/150 is the more common current recommendation, and studies have shown that for quite cold or hot areas 1/100 (1%) open area does a much better job of controlling moisture and attic heat.

In houses with attic living spaces, unless the entire attic is "conditioned space", those openings still exist plus there should be gaps over the top of the attic living space insulated walls so the air in the low "crawlspace" portions of the attic does not get isolated and be able to build up moisture or excess heat.


If you mean a gap, per image above, between the exterior wall sheathing and/or board insulation (if you have that) and the siding, you may have a ventilated siding or "rain screen wall" contruction - where the siding (which is a water shedding system, NOT waterproof) "stands off" from the wall and the water barrier (housewrap) to provide a gap for any water getting in through the siding (common with lap sidings, especially non-wood ones). It is designed to drain any infiltrating water down behind the siding and drip out to the ground from the drip edge flashing underneath the bottom row of siding, and also to provide an airflow behind the siding to allow evaporation of moisture that gets blown in there in storms. The "rainwall" or "rainscreen" design, except in very consistently wet areas like rain forest areas or windy rainy coastal areas for examples (which may have a true water/vapor barrier behind the siding instead of under the interior drywall), is basically designed assuming occasional water will get blown in through the siding, but the gap behind will than dry out between windblown rain events without causing significant damage.

This gap, which is commonly formed by nailing firring strips (preferably treated wood) over the housewrap or vapor barrier (as applicable) and into the studs, allows for airflow for evaporation and also, because the siding and wall are not in significant direct contact (only at the firring strips) minimized the opportunity for mildew/mold formation and eventual rot at that point. Some systems use a metal or plastic firring strip, or specific standoff bulges on the siding to minimize the contact between siding and wall.

One other thing this gap does, in hot areas, is vent heat from the siding up and out the top (though that does go into the attic but is usually a small heat contributor there, compared to the roof itself), making for a cooler wall and less air conditioning need. In very hot areas that gap may be enlarged from the usual 1/2 - 3/4" to as much as 1-1/2" to promote siding ventilation.

With this sort of system, while you would not likely be able to see "daylight" in the gap, you would get some indirect light penetrating through the overlaps in the siding - especially with factory formed plastic or metal lap siding, which commonly has a bit of a gap between the overlapping pieces.

Obviously, any light should only be coming in "upward" under the siding - direct or downwards directed light would indicate a place water could easily infiltrate. If light is coming in through end joint gap between siding planks, then they forgot the "siding butt joint back flashing" - water barrier strips (ice and water shield or special gap filler pieces) which go in behind the joint and serve to redirect any infiltration at the expansion joint back out onto the top of the underlying plank.


If you are talking something other than these (and of course you can ask your builder to explain the gap or daylighting), you can respond back with more info using the yellow Answer This Question button right below your question. You can attach photos if you desire (GIF, JPG, JPEG, PNG formats only) using the left-most yellow gray header bar icon on the "Answer Question" page which pops up when you click that button.

Answered 2 years ago by LCD

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