Attics and crawlspaces are like some members of the family – you know they’re there, but you’d just as soon not deal with them unless you have to. But for those occasions when you do have to make that dreaded crawl, it pays to have convenient access. In fact, most building codes are very specific about access sizes, locations and other particulars that help make getting into and working in these areas a little safer and easier.


If your home has a raised foundation, the foundation stemwalls and the framing for the floor create a space under the house – a space referred to in the building codes as the “under-floor space,” but more commonly known in the trades as a crawlspace. Crawlspaces typically have quite a few building components in them – wiring, plumbing, ducts, and sometimes heating equipment – and access is a definite necessity.

Most building codes require an access hatch that is 18 inches by 24 inches in size. That size increases to 20 by 30 inches if there is equipment such as a furnace located in the crawlspace (see below). Typically, two cross members are installed between and perpendicular to two floor joists to create the rectangular opening, but in some instances a joist may have to be cut and framed with a header in order to achieve an opening of the proper size or in the proper location.

Most codes do not specify if the opening is inside or outside of the house. However, in cold climates the access hatch is typically placed inside – usually in the floor of a centrally located closet – in order to limit cold air entering the crawlspace. If you place the access outside, be sure it is insulated and weatherstripped against both the elements and intrusion by insects or small animals.


Attic accesses are required for any attic that has a clear ceiling height of 30 inches or more, and the opening needs to be a minimum of 22 inches by 30 inches in size. Note that one dimension is 22 inches instead of 24 inches – the building codes have made this adjustment so that access holes will fit between commonly used roof trusses, which are usually on 24-inch centers.

Here again, the codes don’t typically specify inside or outside access. Many older homes have outside access hatches placed in a gable end, but in newer homes it’s much more common to find them inside – again, typically in a centrally located closet. If the access is inside, a dam must be constructed inside the attic so that it surrounds the opening and prevents blown insulation from falling into the hole. Also, the access hatch must insulated to the same level as the surrounding attic, which is usually done by attaching a batt of insulation to the attic side of the hatch cover.


It’s not uncommon to find large pieces of equipment such as furnaces, water heaters, pumps, and other equipment – generically called “appliances” in most building codes – located in the attic or the crawlspace. In these instances, there are some additional building code requirements that you should be aware of.

First of all, most codes state that an appliance must be “accessible for inspection, service, repair and replacement without removing permanent construction” – simply put, if you have to work on or replace your furnace or other equipment, you need to be able to do so without cutting a hole in the floor or the ceiling.

Additionally, “30 inches of working space and platform shall be provided in front of the control side to service an appliance.” This means that in an attic you will need to have a piece of plywood or other suitable material placed over the ceiling joists in front of the appliance on the side where the controls and access panels are located so that you create a platform to kneel or stand on while working, and that platform needs to extend out from the appliance a minimum of 30 inches and be at least the width of the appliance itself.

In attics with appliances, the access hole is still a minimum of 22 by 30 inches. In addition, the appliance needs to be located so that there is a clear passageway from the crawl hole to the appliance, and that passageway needs to be a minimum of 22 inches wide and 30 inches high.

In crawlspaces with equipment, the access hole size increases to 20 inches by 30 inches. Here again, you also need a passageway from the access hatch to the appliance that is 20 by 30 inches, and a minimum of 30 inches of clear working space on the control side of the appliance.

Another building code requirement to be aware of is that a permanent light fixture must be provided in the attic or crawlspace if there is equipment installed there, and a second light near the equipment itself for servicing. Also, an electrical outlet needs to installed within 25 feet of the appliance for use during servicing, and in crawlspaces that outlet needs to be a ground-fault circuit-interrupter (GFI).

Remember that the building codes can vary between jurisdictions, so always check with your local building department for specific requirements prior to doing any work.


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