No Crawl Space Ventilation

I have been inspecting several homes in Montana that were built in the early 1900 and have a partial cellar with a partial 3 foot crawl space. The issue I am having is there is no ventilation in the crawl space. Per standards you should have 1/300 ventilation. The weather in western Montanan is very low humidity and the homes do not have any signs of moisture problems. Makes it hard to call out a defect in ventilation when the house has been there for 100 years with no issues.

Does anyone have any input on this or seen this before?

Thanks Dan

Ask the buider Tim Carter seems to give good advice & information.

Wasn’t required when it was built, why would you hold it to current standards?

i agree with this in this situation.

maybe say something like “although no vents were found, ventilation appeared adequate at time of inspection”

The need for ventilation of crawl spaces varies widely depending on local conditions.

I personally live in a house that is 140 years old with a limestone/brick foundation basement and a 1971 addition with a crawl space with CMU. foundation. The crawl space is does not have a vapor barrier and is not ventilated. After 35 years, this non-ventilated and non vapor barriered crawl space has no evidence of excess moisture or WDO. The adjacent basement does show evidence of dryrot and sistered floor joists. The “floor” also does not have a vapor barrier and was no insulation until appx 10 years ago when I purchased it.

So what’s the point? Your milage may vary with regard to ventilation requirements you are exposed to on this board. Critical factors are - local building codes, foundation drainage, soil conditions, local weather conditions etc. Be aware of what is needed where you inspect.

Here are some resources to increase your knowledge. An AIA document(PDF) which is a summarry and contains excerpts from a 88 page PATH/HUD document(link below).

Ventilation AIA 18-22-01.pdf (243 KB)

This situation is unique, and I agree it is hard to call it as a defect, when 100 years of evidence show no damage as a result.
I would note that I observed no vents installed, and that no visible evidence of moisture condensation, etc. was found as a result. Basically to inform the buyer what the standards are, but to also let them know that I did not see a material defect as a result of their absence.
The reason I note such conditions is that when they bring a contractor into to do other home improvements, or they sell the house a year later and another inspector tells them they need vents then they will have some understanding about the issue, and not be surprised, …assuming I missed a serious problem.
You know the last man in theory…they are alway going to believe the last man. But if I can educate the client ahead of time, I believe it reduce chances that they will ask me to pay for something that does not need to be done.

I do not like vented crawlspaces in Massachusetts.

The vents are great if you like water intrusion/mold/high dewpoints.

I agree with David. Even though vents are required around here, typically, we shut them and stuff 'em with insulation, insulate the perimeter of the crawlspace and stick a heat duct or two down there.

This link has good information regarding a closed crawlspace and some options. The thinking on crawlspace ventilation is changing to more positive moisture control. The picture shows what happens when a crawlspace has no vapor barrior and the vent(s) were closed. It is mold.

Crawl Space Mold4.jpg

I inspect in a similar, low humidiy environment, and I see many new homes built with no ventilation in the crawl, or weep holes in brick veneer. The building code enforcement doesn’t seem to mind, but even in low humidy, or especially in low humidity climates where an evaporative air conditioner is used, there is considerable moisture that can condense and encourage WDO. I stuggle with writing these up, but I do not find wisdom in blocking off vents. Why are some of you suggesting the vents be blocked?

Any crawl space should be either well ventilated, conditioned/heated, or completely sealed off (not as common).

There have been mold, wood rot, and other problems in older homes that have crawl spaces without good ventilation. The severity depends on the local climate, with less problems for older homes in drier areas without floor insulation or tight construction. The space had some ventilation and was somewhat conditioned/heated due to the lack of insulation without a vapor barrier facing at the floor framing.

BUT, take that same older home and seal up gaps and add modern insulation with a vapor barrier (e.g. tar layer on the back side of modern paper faced batts) … a common thing homeowners do to “fix” cold floors above crawl spaces … and you have a recipe for problems, particularly for older dirt floor crawl spaces.

In one crawl space in an older home without adequate ventilation where the homeowner added faced batts insulation between the floor joist bays, my awl went completely through the bottom 2" of the wood framing due to stagnant unheated conditions created by adding the insulation … :shock: