Should i vent my crawl space

This idea might work if done in new construction where there is a level ground with stable soils. The problem with doing a concrete slab as a retrofit is typically in the application. Most crawl spaces are difficult to access, making proper concrete pouring and curing difficult. Not to mention the fact that concrete is extraordinarily expensive and may not solve all the moisture issues that would occur as moisture could potentially be drawn up through the concrete or through cracks and crevices.

The best solution is to have the crawl space encapsulated using a thick at least 10 mil vapor barrier. This barrier will need to be adhered to the foundation walls with glue and all the seams taped. Almost half of the air we breathe on the first floor of our home comes from the crawl space.

A dirt crawl space with open crawl space vents is a never-ending source of moisture. Even if the dirt's surface seems dry, digging down a few inches reveals moist earth. This moisture is constantly released into the crawl space. It's the moisture that causes mold growth , musty odors, and eventually structural damage, not to mention that insects and critters love moist environments.

Additionally, energy costs are higher. Moisture ruins houses by providing a hospitable environment for mold and other fungi, and insects that destroy wood framing. Crawl space moisture, and the mold and mildew that thrive in this environment, affect not only the floor system directly above, but also the entire house.

Three things destroy organic materials such as wood or insulation: water moisture or high relative humidity , heat, and ultra-violet radiation. Of these, water is by far the most damaging. If you decide to not seal off crawl space vents year-round, the simplest way to close your crawlspace vents for the winter is to plug them from the outside with foam blocks made specifically for crawlspaces. Then remember to remove the plugs when the weather turns milder in the spring - and as you do so, check to make sure that your crawlspace vent screens are intact so that insects and rodents don't make nests under your home.

You could also choose to go with automatic vents, which are designed to work without electricity, and open at approximately 70 degrees and close at around 40 degrees. If you are experiencing mold in your crawlspace, there are several solutions you can look into for dealing with the moisture issue that led to the mold growth. Adding supply air from the HVAC system is tricky and may let the crawl space humidity go too high in spring and fall.

Was I Dreaming? Therma-Stor dehumidifiers. There are many terrific There are many terrific articles, including yours, on encapsulating the crawl.. However there is an alternative, that is moving the pressure and thermal boundaries to the bottom of the floor joist, air sealing and leaving the venting or increasing it. Have you spoken to this solution..? Good article Allison.

They are dropping termite bonds left and right these days for improperly done crawlspaces where insulators are covering the stem walls all the way up to the subfloor, or even spray foaming the subfloor and covering down the band board. This promotes a great air seal, but hides a real problem. The cost of option 2, supply The cost of option 2, supply air from the HVAC system, looks to be nearly zero to me what is the cost of one hole?

The capital cost and the operating cost of option 3, dehumidifier, are significant. I suspect that future building scientists will scoff at our attempt to treat a crawl space like a regular room in the house. It is not. I remain skeptical. I suspect that there are some missing data in the calculations. Do you have any opinions on these claims? But why did I embarrassingly today encapsulate my small crawlspace in ? To get rid of the damn chipmunks.

When I encapsulated there was a musty smell and a light white dusting on the floor joists. Six months after encapsulation the space was bone dry with no musty smell.

Near-dewpoint equilibrium was apparently due to moisture diffusion though the hardwood floor and perhaps a little supply air duct leakage. I recall a Canadian code or design guide which appropriately said to close crawlspace vents in the summer unless you wanted to humidify the crawlspace.

In some homes this could be near the mold proliferation RH! Bailes, you need to Dr. Bailes, you need to escape your southern parochialism and visit places where hockey is played by real hockey players.

Transfer grilles work just fine in such locations. The point needs to be made that moisture has to be removed from the crawlspace. That can only be done with dilution with drier air or with a dehumidifier. With the former approach some type of air change is needed with the conditioned part of the house where dehumidification is occurring either via the operation of an air conditioned or via dilution ventilation with outside air when the outside air is drier than the inside air.

If it is not clean then you should not do so. In trashed crawlspaces sucking on them with a continuous exhaust fan works well. In clean crawlspaces up north transfer grilles work just fine. In between and in the south a very small amount of return air works fine with a transfer grille as does a small amount of supply air with a separate fan that does not blow cold air from the HVAC system that Mr. Gatley guy knows a few things about physics but blows house air that is warmer and drier.

Allison, Allison, Hope you or Joe L. Because the floor system will be open-webbed trusses, getting insulation against the warm floor and keeping it there is problematic. The stem walls will be ICFs with an R value. I have suggested we have an unvented crawlspace with a sealed membrane on the dirt that is also sealed to the ICF stem walls to keep radon out of the envelope. The main reason for the unvented space is not to keep moisture out but to negate the need for insulation in the floor assembly.

We are at HDD so cold dry air in the winter is more of an issue than moisture. There will be plumbing runs and ductwork in the crawl space but no mechanical equipment. The band joist will be sprayed foam. Am I on the right track here? Another great article, Another great article, Allison. But I see a dehumidifier as a method-of-last-resort. This is one of those building science topics where smart people may disagree.

Airing it out in forums like this is a great way to move toward best practice. You should be skeptical. Energy savings claims are very much dependent on climate and circumstances, in particular, whether ducts are in the crawl. But if energy savings and first-cost is paramount, best to eliminate the crawl and either build a finished basement or slab-on-grade. In a cold climate and no mechanicals in the crawl, the floors may get a bit cool due to influence of cooler ground.

I have a project in eastern Long Island with radiant floors over a closed crawl, with AC ducts in the crawl. If the thermal envelope aligns with foundation wall rather than floor, the radiant system will lose too much heat to the crawl, increasing heating costs.

They decided to insulate both walls and floor, but I advised some air exchange between crawl and house. I think you have a good I think you have a good approach. I would have a small 4 inch supply duct supply air to the crawlspace and have two transfer grilles connecting the crawlspace to the house. Our website has more information on this. That Mr. Butler fellow also knows what he is talking about.

Not sure about that turpentine stuff he puts on his pork though….. Allison, Allison, Your customarily thoughtful and informative observations are always welcome. I try to precede all my interweb comments with something positive. It has a lulling effect Exterior vents were foam sealed and additional insulation was added to a few wall areas in need. The vapor barrier is probably not as continuous as it needs to be, but regular visits to the netherworld have revealed no condensation issues.

Annual radon tests free through the Agricultural Extension Office have the been just below the threshold but at age 69, I will doubtless die from something beside lung cancer anyway.

Benefits include bare-foot comfortable hardwood floors, no more mice wintering over through the hole in the vent left by the cable guy three hours clean-up with a shop vac , no more dirt in the CS blown in by our Washoe Zephyers and no annual fussing with vent dampers. Energy use changes have been undetectable on a purely anecdotal basis.

Totally DIY but without the supply duct, would have been a big deal. No actual engineering was involved in this project and any unintended negative consequences have been below the threshold of detection. Best wishes. Regardless, in our dry CA climate we have had very good results with installing a sealed ground source vapor barrier directly on the soil, sealed to the foundation walls, then sealing up all perimeter venting, and providing exhaust ventilation at code minimum.

Reed D. I met a guy from New Jersey or was it Delaware? Jamie K. Johnson : Yes, that hybrid approach would get you the best of both worlds. Then the DH would be down there when you need it during cool, rainy periods in summer, too like we had most of this summer in Atlanta. Barry W. Matthew R. How will a sub-poly ventilation system affect the air above the poly? Don G. Your 5 points contain a lot of great points. About your home, though, I think maybe you got lucky. At the end of the day, you need to fix the crawl space vents if you want to avoid crawl space moisture as a whole.

The only way to fix it is to remove the source of the problems. Now that you know what typically causes crawl space humidity, do you know how to fix it?

These are the most important steps to take when it comes to solving your crawl space humidity problems. First off, you need to make sure you have a fully closed crawl space. If you have crawl space vents, you need to install crawl space vent coverings, and if you have crawl space doors that open to the outside, you need to make sure the insulation around the doors are solid. The next step should be to install vapor barrier liners. A vapor barrier liner goes on the ground, up the walls, and around any supporting struts in your crawl space.

Plus, with a strong liner like a mil liner, people will be able to go into your crawl space to inspect it in the future without damaging the liner. In many crawl spaces that have been left unattended for months or years, the insulation and ducting are completely trashed. Moisture can seep into the insulation and ducting, then make it dissolve, whether due simply to the moisture or due to mold and mildew.

It may be up to you to replace all this broken and worn-down insulation and ducting. Insulation is also very important because it can help you avoid crawl space moisture and similar issues. Think about it: With insulation around cold water pipes, for example, you can avoid condensation on the pipes.