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Daler 10-21-2010 03:32 PM

Crawl space vents -- joist cut out!
 
2 Attachment(s)
The few crawl space vents we have we wish to make most effective. The rancher is 30 years old.

I found that the builder cut out part of the rim joist to accommodate the 8x14 vents (also formed as part of the concrete foundation).

A couple of questions:

At a foot from the corner, is a rather rude 2/3 cut-away in the rim joist. Is this structurally ok? -- it has been there for 30 years with no apparent affect to the structure. If not what to do to bolster it?

Also, the adjacent joist is only 8" from the rim joist. I think more air flow access would be good. I was thinking about also notching out this adjacent joist but am leary about screwing with the structural integrity.
So, what else can be done to both open the area up more and keep the strength of the floor in that corner (bedroom)?

Daniel Holzman 10-21-2010 05:14 PM

Your rim joist is directly supported by the block, as such a notch such as you have is not structurally significant. However, cutting the same notch in an adjacent joist that is supported only on the ends would be a very serious mistake, as it would effectively destroy the structural value of the joist.

Red Squirrel 10-21-2010 06:05 PM

I never understood crawlspace vents. My crawlspace is completely sealed from the outside, is treated as conditioned space and other then some spider webs that I have to remove every now and then it's very clean. When I have the money I want to insulate the rim joists properly and even add foam to the walls, then studs, then more insulation. This should cut down on the spider webs and be more efficient for heating. Clutter is also bad for spiders, I need to get rid of all cardboard and use plastic for storage. But from my understanding the vents are a US code so guess you have to have them to be compliant...

As for the notch that looks ok as the whole member is supported by the wall, as mentioned above.

Ron6519 10-21-2010 06:19 PM

Sorry, I don't see anything supported by the wall. I see a joist against a foundation wall cut to crap, the truncated end resting on the wall.
I would drill 4 holes through the cut joist(2 on each side) , and epoxy 1/2" threaded rod into the foundation wall. Secure with nuts and washers.
Ron

Gary in WA 10-21-2010 06:34 PM

It appears that 4" high notch in a 2x10 joist is against the concrete wall where there should be a mud-sill bolted down. The sub-flooring would span from the 8" away joist (un-notched) to the sill plate. Possibly 10-12" span. I don't see the joist (notched) having much weight on it. I would leave it if the sub-flooring rests on top of the sill plate, under the wall.
The horizontal board marks in the concrete date it older than 30 years....... where are you located? Unless done by a DIY'er....

Gary

Daler 10-21-2010 08:51 PM

The joist is not supported by the top of the foundation, it is directly adjacent to it, on the face. That part of the foundation is stepped up (from the adjacent wall) and includes the cast-in vent, with a cement-stained 3/4" ply box embedded in it (can that plywood box be removed to further open up the vent??). The 2x4 wall plate is on top of that. The subfloor, et al, rests on both the plate and the notched joist. Btw, the wall in question is the gable end of the trussed roof house.

So yes, after thinking about it, there is probably very little weight bearing down on it.

However, I guess I could through-bolt it to the foundation that's up against it. But could I not instead add bridging to the next joist? Or box it out with headers to the next joist(s)? -- I figure that could open up the breathing area for the venting if that is really an issue. Which leads back to wondering if the current configuration really is an venting barrier issue, especially if I want to add an exhaust fan to the opening??

And yes, this is the original pro build spec from 1979. I'm located in Victoria, BC (Pacific Northwest).

Gary in WA 10-21-2010 09:48 PM

With the 4" notch, you still have 5" of meat above. If worried, add a 2x4 across the joist bottoms 4' long to carry the long end (opposite the beam end). Why are you opening the vents more?

Do you have a vapor barrier on the ground: http://dirt-crawl-spaces.com/crawlspace-venting.html

http://www.energy.wsu.edu/documents/...awl_Spaces.pdf

Welcome, neighbor, I’m South of Seattle.

Gary

Daler 10-22-2010 12:47 AM

Quote:

Originally Posted by GBR in WA (Post 520990)
With the 4" notch, you still have 5" of meat above. If worried, add a 2x4 across the joist bottoms 4' long to carry the long end (opposite the beam end). Why are you opening the vents more?

Do you have a vapor barrier on the ground: http://dirt-crawl-spaces.com/crawlspace-venting.html

http://www.energy.wsu.edu/documents/...awl_Spaces.pdf

Welcome, neighbor, I’m South of Seattle.

Gary

Seattle's a great place to visit, Gary ..although we haven't been there in many years.

Your weather is similar to ours. However, methinks it's more like Vancouver.
Victoria is drier, hense a major reason why we moved here from the Mainland.

No, the notch in the joist is about 6.5" deep/high -- 14" across.

As for the vents, there are only three 8"x14" vents in an 1800 sq ft crawlspace. Humidity is a bit of a concern here with RH steady at 67° (was at 90° until dehumidifier established a baseline). Anyway, the CS is a "cold" type which we want. A conditioned space will require way too much work + it will have to be heated = $$$. If need be I will either add another vent somewhere in the rim joist or put in an exhaust fan ..we'll see how it breathes after this is done.

After living here for 10 years, we are finally getting the joists reinsulated to full cavity (R32) (too cold floors). During the process of working in the CS (cleaning out, etc) I discovered myriad of problems, which are now being remedied.

The floor is parged cement over heavy poly -- which is sealed to the foundation/footings.

Wildie 10-22-2010 04:21 PM

Quote:

Originally Posted by Daler (Post 520962)
The joist is not supported by the top of the foundation, it is directly adjacent to it, on the face. That part of the foundation is stepped up (from the adjacent wall) and includes the cast-in vent, with a cement-stained 3/4" ply box embedded in it (can that plywood box be removed to further open up the vent??). The 2x4 wall plate is on top of that. The subfloor, et al, rests on both the plate and the notched joist. Btw, the wall in question is the gable end of the trussed roof house.

So yes, after thinking about it, there is probably very little weight bearing down on it.

However, I guess I could through-bolt it to the foundation that's up against it. But could I not instead add bridging to the next joist? Or box it out with headers to the next joist(s)? -- I figure that could open up the breathing area for the venting if that is really an issue. Which leads back to wondering if the current configuration really is an venting barrier issue, especially if I want to add an exhaust fan to the opening??

And yes, this is the original pro build spec from 1979. I'm located in Victoria, BC (Pacific Northwest).

The source of moisture in crawl spaces is through the vents from outside.
I have closed off all vents in my crawl space and added heat/cooling registers to make the crawl space part of the conditioned space of the building.
Here in Canada its recommended that crawl spaces are not vented to the outside.
Since I closed mine off, its been drier than the Sahara desert.

Daler 10-22-2010 04:41 PM

Quote:

Originally Posted by Wildie (Post 521383)
The source of moisture in crawl spaces is through the vents from outside.
I have closed off all vents in my crawl space and added heat/cooling registers to make the crawl space part of the conditioned space of the building.
Here in Canada its recommended that crawl spaces are not vented to the outside.
Since I closed mine off, its been drier than the Sahara desert.


Thanks for you comments about a conditioned CS. This seems to be a bantered topic in many forums.

But wouldn't this amount to making the space a mini-basement?

I'm not sure it's worth the effort and big expense to do that when I can just reinsulate the floors to R32, add more insulation to the pipes, and open the vents ..or maybe add a couple more vents or, if needed, minimal mechanical ventilation such as http://www.tjernlund.com/Tjernlund_UnderAire_Crawl%20Space_Ventilator%20Lit _8500720.pdf

Having the vents open has served us well in the past. It's only in this last year that we had an RH problem that pointed to perimeter drain sag (now corrected), irrigation sprinklers close in to the foundation vents (now corrected). As well, most of the downspouts have now been turned out into the garden.

Our mild climate is not that damp -- very few really cold days and a lot less rain than even Vancouver! Summer humidity is almost non-existant with the prevailing winds, etc.

Sheesh .. if I find this doesn't cut it then we may look for other solutions.

Wildie 10-23-2010 12:16 PM

Quote:

Originally Posted by Daler (Post 521396)
Thanks for you comments about a conditioned CS. This seems to be a bantered topic in many forums.

But wouldn't this amount to making the space a mini-basement?

I'm not sure it's worth the effort and big expense to do that when I can just reinsulate the floors to R32, add more insulation to the pipes, and open the vents ..or maybe add a couple more vents or, if needed, minimal mechanical ventilation such as http://www.tjernlund.com/Tjernlund_UnderAire_Crawl%20Space_Ventilator%20Lit _8500720.pdf

Having the vents open has served us well in the past. It's only in this last year that we had an RH problem that pointed to perimeter drain sag (now corrected), irrigation sprinklers close in to the foundation vents (now corrected). As well, most of the downspouts have now been turned out into the garden.

Our mild climate is not that damp -- very few really cold days and a lot less rain than even Vancouver! Summer humidity is almost non-existant with the prevailing winds, etc.

Sheesh .. if I find this doesn't cut it then we may look for other solutions.

But wouldn't this amount to making the space a mini-basement?

Thats exactly what happens!

In my crawl space, I covered the inside of the crawl space with R12 ROXUL with a 6 mil v/b over top, all around the perimeter.
The insulation is held in place with insulation mounting pins. These pins have a perforated base and are fastened to the concrete with construction adhesive.
Using this method, no framing is required to mount the insulation and v/b.
The job is straight forward, no fiddling around trying to insulate ductwork, placing v/b and insulation between the floor joists.
I do have 6 mil plastic over the earth floor.

Gary in WA 10-23-2010 01:36 PM

Insulating the floor may be cheaper to heat than insulating the walls, notice tests done in Flagstaff: http://www.advancedenergy.org/buildi...l%20Spaces.pdf

Closed crawls are not for everyone in a cold climate, check with your local Building Department: “However, unvented crawlspaces aren’t recommended in certain locations. For example, a warm crawlspace in an extremely cold climate may eventually melt the perma-frost beneath the home, allowing the home to sink into the ground. Also, when homes are built in high water table areas (near rivers at the bottom of steep valleys, for example), it can be useful to seasonally vent the crawlspace to allow for drying after flooding. “
http://www.eere.energy.gov/buildings...s/db/35379.pdf


One way to insulate at the vent, pp3: http://docs.google.com/viewer?a=v&q=...P2rnn9nxm8UjuA
Good info on radon and how to control it.

For other readers, check with Officials before converting to a closed crawl: http://energy.cr.usgs.gov/radon/rnus.html

If you do change it over, bring it up to minimum safety code, you will need: a vapor barrier; continuously operated mechanical exhaust ventilation; and conditioned air supply:
http://www2.iccsafe.org/cs/committee...E_06_64_07.pdf

Sorry to get off track, just want to cover all the bases for others reading...
Gary

Daler 10-23-2010 01:54 PM

Quote:

Originally Posted by Wildie (Post 521783)
But wouldn't this amount to making the space a mini-basement?

Thats exactly what happens!

In my crawl space, I covered the inside of the crawl space with R12 ROXUL with a 6 mil v/b over top, all around the perimeter.
The insulation is held in place with insulation mounting pins. These pins have a perforated base and are fastened to the concrete with construction adhesive.
Using this method, no framing is required to mount the insulation and v/b.
The job is straight forward, no fiddling around trying to insulate ductwork, placing v/b and insulation between the floor joists.
I do have 6 mil plastic over the earth floor.


Where in Canada do you live, Wildie?
Besides the RH factor, there's the comfort vs cost level. What's your temp difference up vs down -- how warm are your floors?

Our CS is with sprayed concrete over 6 mil poly and sealed at the foundation. Our house is electric baseboard heating with a standalone HRV (mounted remotely in the garage). The HRV insulated ducts are attic run to ceiling vents. This keeps the upstairs of our rancher quite comfy and dry.

However, if we were to instead "condition" the CS (by closing the vents and draping the foundation walls with an insulated product) then would I not have to essentially heat the CS with myriad of baseboard heaters (and find another free 220v circuit) in order to also keep the above floors warm (now there would be no or little insulation in them)? That could prove a real ongoing expense.

I'll concede that the dew point in the CS can be more accurately controlled by regulating the space, but I am at a loss as to see how this can also keep my utility bills the same or better.

My reasoning was to instead insulate the heck out of the subfloors instead and provide lots of air movement in and out of the CS. But I can definitely see your point of warm summer air condensing in the CS. But wouldn't either closing those vents in the summer or providing good (mechanical?) ventilation achieve the same result?

Another thought I had was to incorporate a sort of hybrid approach : insulate the subfloor as planned, close off the vents, route an HRV fresh air supply (only) into the space with a small exhaust fan at the opposite side of the CS moving CS air to the outside. The fan would be sized equal to the incoming supply air. This would be relatively easy to accomplish in our situation.

The last point of concern is to mitigate chances of any migration of polutants into the living space from the CS.



It would help with this discussion if others would like to share their thoughts, or I can move this to another thread?? :thumbsup:

Daler 10-23-2010 03:28 PM

Quote:

Originally Posted by GBR in WA (Post 521824)
Insulating the floor may be cheaper to heat than insulating the walls, notice tests done in Flagstaff: http://www.advancedenergy.org/buildi...l%20Spaces.pdf

Closed crawls are not for everyone in a cold climate, check with your local Building Department: “However, unvented crawlspaces aren’t recommended in certain locations. For example, a warm crawlspace in an extremely cold climate may eventually melt the perma-frost beneath the home, allowing the home to sink into the ground. Also, when homes are built in high water table areas (near rivers at the bottom of steep valleys, for example), it can be useful to seasonally vent the crawlspace to allow for drying after flooding. “
http://www.eere.energy.gov/buildings...s/db/35379.pdf

Great article -- thanks. You have obviously been down this road :thumbup:

So it seems even macro location can be a determinant. Our climate is not that cold ..or hot. It's quite moderate -- hardly ever any ground frost and not much humidity in the summer. This is why I lean towards keeping the vents open. However, if they are closed then obviously some sort of replacement ventilation is needed. Hense, my suggestion of taking a small trunk off of the HRV supply line (but how to guage the proper duct size??).

It also seems by their previous and latest studies there appears not a great difference in RH efficiency whether insulating between floor joists or insulation-draping of the foundation walls. In fact, they suggest that colder climates benefit most from having insulation up in the floor joists instead of the foundation walls -- in the winter the 2000 sq ft. living space will radiate quite a lot of heat into the uninsulated concrete CS floor ..a big heat-sink. BTW, we have no ductwork in the CS, only plumbing and electrical.



One way to insulate at the vent, pp3: http://docs.google.com/viewer?a=v&q=...P2rnn9nxm8UjuA
Good info on radon and how to control it.


I had that vent baffle in mind by using Isoboard (styrofoam+). Not aware of any known Radon gas problem here on Vancouver Island.


For other readers, check with Officials before converting to a closed crawl: http://energy.cr.usgs.gov/radon/rnus.html

If you do change it over, bring it up to minimum safety code, you will need: a vapor barrier; continuously operated mechanical exhaust ventilation; and conditioned air supply:
http://www2.iccsafe.org/cs/committee...E_06_64_07.pdf

Sorry to get off track, just want to cover all the bases for others reading...
Gary

No, this discussion is what I need before spending a $2000+ bill on reinsulating the CS. I just hate correcting things after the fact :wink:

Michael Thomas 10-23-2010 06:12 PM

GBR,

Hey... that http://crawlspaces.org/ link is a good resource, and new to me.

Thanks!


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