Just had my crawl space inspected and it’s missing some blocks down there and the insulation needs to be replaced, it’s outside under my porch and it’s no mold or water down there but I’m looking to buy this home but I wanna second opinion of what I’m up against and is it worth it. It’s a good neighborhood and at a good price PLEASE HELPenter image description here

  • 5
    Is it possible that/those openings are used as air vents? Hard to tell just from that picture, but might only need vent covers/screens.
    – crip659
    Nov 29, 2021 at 21:00
  • Why do you need insulation under your outside porch?
    – Lee Sam
    Nov 29, 2021 at 21:41
  • 1
    "Is it worth it" is something only you can determine.
    – FreeMan
    Nov 30, 2021 at 0:03
  • 1
    Based on Lee Sam's answer voting to reopen. It does, though, still need some additional clarification.
    – FreeMan
    Nov 30, 2021 at 13:26

2 Answers 2


I disagree with @Freeman, you are not the only one who can decide if it’s worth fixing the area with the missing blocks. The code can help determine if you need to fix it too.

The code requires an opening into the crawl space that is a minimum of 18” x 24” or if through the exterior wall a minimum of 16” x 24”. (See R408.3)

In addition, your crawl space is required to have 1 square foot of ventilation for each 150 square feet of crawl space AND 1 such vent shall be within 3’ of each corner. (See R408.1) The access opening can be part of the required ventilation, if covered with appropriate ventilation material. (See R408.2)

Btw, there are several exceptions including eliminating vents on one side, eliminating all vents if the crawl space is mechanically vented, etc. (See R408.2 exceptions)

Review these items on site and you’ll know if it needs to be fixed/improved.

  • 1
    Great answer. I would never have guessed there are code specs for a crawl space!
    – Leroy105
    Nov 30, 2021 at 3:30

The opening does look like for the purpose of venting, but a grille is missing. This is a minor defect and quite easy to fix, however, more importantly, you shall make sure the crawl space construction meets the building code requirement. If your local jurisdiction has adopted IRC (International Residential Code), it does have requirements for venting the crawl space, the relevant code provisions are provided below for your information:

1) The IRC prescriptions for venting crawl spaces are contained in section R408, in several paragraphs. The first paragraph of IRC section 408 provides the standard requirement for ventilating crawl spaces:

The under-floor space between the bottom of the floor joists and the earth under any building (except space occupied by a basement) shall have ventilation openings through foundation walls or exterior walls. The minimum net area of ventilation openings shall be not less than 1 square foot for each 150 square feet of under-floor space area, unless the ground surface is covered by Class 1 vapor retarder material. Where a Class 1 vapor retarder material is used, the minimum net area of ventilation openings shall be not less than 1 square foot for each 1,500 square feet of under-floor space area. One such ventilating opening shall be within 3 feet of each corner of the building.

2) The second paragraph provides details of how these crawl space vents should be structured. Each vent must be at least 1 square foot in size and allowable materials include:

  • Expanded sheet metal plates not less than 0.047 inches thick

  • Perforated sheet metal plates not less than 0.070 inches thick

  • Cast-iron grill or grating

  • Extruded load-bearing brick vents

  • Hardware cloth of 0.035-inch wire or heavier

  • Corrosion-resistant wire mesh, with the least dimension being 1/8-inch thick

If you are using a ground vapor barrier, the vents can be of the type that has moveable louvers.

3) The third paragraph makes provisions for situations in which builders and homeowner prefer to omit vents in crawl spaces, usually because they wish to prevent thermal heat loss or to prevent insects and other vermin from gaining access to the crawl space.

Builders are now allowed the option of creating non-vented crawl spaces, provided they follow the following procedures:

  • Mechanically circulating air should be established between the upper conditioned area of the home and crawl space.

  • The air-circulating device must move at least 1 cubic foot of air per 50 square feet of crawl space area.

  • The crawl space floor area must be completely sealed with a vapor-retarding material.

  • The edges of the vapor retarder must be lapped up against the inner foundation walls. Overlapped separate sheets must be lapped at least 6 inches. The seams must be sealed.

  • All crawl space walls must be insulated to appropriate R-values for the regional climate.

Finally, an article with an opposing view on the requirement of crawl space venting is linked here for readers who reside at locals that have not adopted IRC and do not have a clear requirement from the local ADJ, to consider. (Note, this article is provided for information only, it does not represent my endorsement on the stated method nor the commercial statements)

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