Water on garage footer

[dankoos]

I own a small ranch home built in 70's that sits on a crawl space. The crawl has poured concrete floor, no major issues down there, a little water that seeps in when we have a lot of heavy rain. At some point, a garage was added to the home. The block is about 3 deep under ground and 3 more above ground forming the first 3rd or so of the garage wall. With all the rain, we discovered the bottom plate of the back wall started to rot out (only a 2x4, untreated). The drywall had a little mold, but wasnt bad. The outside sheeting has no damage. When you look down inside the block, there is 2.5" of standing water sitting down there. We were hoping to convert garage to additional living space. Does a French drain need to be installed outside or can the top of the block be waterproofed with vapor barrier before new properly sized and treated plate is installed before using that block as foundation for new room and not get same water issue? If drain needed, should outside of block be waterproofed as well?

 

[Dana]

An exterior surface drain is always a good idea, but there are work-arounds. Do you know if the rat-slab in the crawl space has vapor barrier under it?

The problem isn't water vapor- it's about capillary wicking of moisture up the CMU block. In ideal builds there is some sort of capillary break material between the wood an cemeticious block or poured concrete. Capillary draw is quite powerful, and can draw moisture from the footing up a full story or more if there isn't adequate drying exposure on the walls. I'm guessing there isn't much above-grade exposure on the foundation wall, and/or the roof overhangs aren't very deep, allowing a fair amount of splash wetting of the above grade exposure.

Jacking up the house 1/4" (a section at at time) is enough to slip in sheet EPDM (membrane roofing or EPDM flashing tape, if it's easier) between the CMU and sills. Most cheap foamy sill gaskets do something, but not nearly as much as sheet metal or EPDM.

If the crawlspace vented to the outdoors? (A bad idea, but common enough in a Columbus OH location.) If there isn't a vapor barrier under the slab it's a good idea to roll out EPDM roofing above the slab as a vapor barrier, and block all venting, then install the current IRC minimum rigid insulation against the EPDM. (In your area that would be R15 continuous foam, or R6 foam + R11-13 in a non-structural studwall butted up to the foam with no interior side vapor barrier, just latex painted wallboard. Code would also require that the crawlspace be ventilated to 1cfm per 50 square feet of floor area- eg a 500' space needs 10 cfm, etc.. The ventilation could be just circulating conditioned space air from the rooms above through the crawlspace, or exhaust-only out the side.

Insulation the foundation walls is a far superior solution than insulating to a code-min R30 between the joists and leaving the crawlspace ventilated. It reduces overall infiltration heating/cooling loads, and it keeps the joists and subfloor from collecting mold-inducing levels moisture when the rooms above are being air conditioned. A foam-only solution (no studwalls) is often easier to deal with in crawlspaces) and can be pretty cheap using reclaimed roofing polyiso or factory seconds foil faced goods held in place by furring through-screwed to the foundation. In OH there are multiple vendors of reject foam (cosmetic blems you don't care about since you're not using full sheets) or reclaimed roofing foam advertising in places like this.

 

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[dankoos]

An exterior surface drain is always a good idea, but there are work-arounds. Do you know if the rat-slab in the crawl space has vapor barrier under it?

The problem isn't water vapor- it's about capillary wicking of moisture up the CMU block. In ideal builds there is some sort of capillary break material between the wood an cemeticious block or poured concrete. Capillary draw is quite powerful, and can draw moisture from the footing up a full story or more if there isn't adequate drying exposure on the walls. I'm guessing there isn't much above-grade exposure on the foundation wall, and/or the roof overhangs aren't very deep, allowing a fair amount of splash wetting of the above grade exposure.

Jacking up the house 1/4" (a section at at time) is enough to slip in sheet EPDM (membrane roofing or EPDM flashing tape, if it's easier) between the CMU and sills. Most cheap foamy sill gaskets do something, but not nearly as much as sheet metal or EPDM.

If the crawlspace vented to the outdoors? (A bad idea, but common enough in a Columbus OH location.) If there isn't a vapor barrier under the slab it's a good idea to roll out EPDM roofing above the slab as a vapor barrier, and block all venting, then install the current IRC minimum rigid insulation against the EPDM. (In your area that would be R15 continuous foam, or R6 foam + R11-13 in a non-structural studwall butted up to the foam with no interior side vapor barrier, just latex painted wallboard. Code would also require that the crawlspace be ventilated to 1cfm per 50 square feet of floor area- eg a 500' space needs 10 cfm, etc.. The ventilation could be just circulating conditioned space air from the rooms above through the crawlspace, or exhaust-only out the side.

Insulation the foundation walls is a far superior solution than insulating to a code-min R30 between the joists and leaving the crawlspace ventilated. It reduces overall infiltration heating/cooling loads, and it keeps the joists and subfloor from collecting mold-inducing levels moisture when the rooms above are being air conditioned. A foam-only solution (no studwalls) is often easier to deal with in crawlspaces) and can be pretty cheap using reclaimed roofing polyiso or factory seconds foil faced goods held in place by furring through-screwed to the foundation. In OH there are multiple vendors of reject foam (cosmetic blems you don't care about since you're not using full sheets) or reclaimed roofing foam advertising in places like this.

I appreciate the lengthy response! To better clarify, this house is a "vacation house" we purchased near Lake Erie. We will not be using in the winter. As for the crawl space under the house, it has vents, but they have been covered up...I was actually just going to remove those for the summer just to get some airflow, bad idea? Also, the main house only currently has baseboard heating and window AC. However, either this year or next we are installing an HVAC system to replace those, but it is going to be installed in the garage along with the new rooms so we need to get our moisture problem in the garage fixed before we do that. Once we have a full HVAC system, we will probably keep the house heated all winter, at least to 50 degrees or so, so we do not have to winterize. Based on what you said, when we jack up the roof to replace the bottom plate of the wall, we should install EMD under our new plate, correct? Do we just drape that all the way down the inside of the block? We also plan on digging outside down to the garage foundation to see what we can see there and install a french drain and/or sump pump if we feel necessary...or is that overkill? I have a sump in my Columbus area house, but that has a full basement.

 

[Dana]

I appreciate the lengthy response! To better clarify, this house is a "vacation house" we purchased near Lake Erie. We will not be using in the winter. As for the crawl space under the house, it has vents, but they have been covered up...I was actually just going to remove those for the summer just to get some airflow, bad idea?

Yes- a terrible idea. In summertime the dew point of the outdoor air is well above the deep subsoil temperature, and the temperature in the crawlspace, and often above the temperature of the subfloor in an air conditioned house. That adds far more moisture to the crawlspace than it purges unless there is no ground vapor retarder and the crawlspace floor is close to the water table.

Sealing and INSULATING the crawlspace walls and band joists to an IRC code-min R15 continuous insulation type performance will keep the crawlspace dry and the joists/subfloor warmer in winter, but also drier and protected from humid outdoor air in summer.

Also, the main house only currently has baseboard heating and window AC. However, either this year or next we are installing an HVAC system to replace those, but it is going to be installed in the garage along with the new rooms so we need to get our moisture problem in the garage fixed before we do that.

There is potentially another issue with putting the HVAC in garage- make sure the entire HVAC system is inside both the pressure & insulation boundary of the house- no ducts or air handler on the "other side" of insulated air sealed walls.

Since you haven't been heating the place in winter there is no way to estimate the sizing requirements based on wintertime electricity use, and you are adding to the space, so you'll have to perform fairly careful load calculations. ACCA Manual-J is something like the gold standard in the industry and is pretty good when done right using aggressive rather than conservative assumptions on everything from air tightness to R-values. IBR methods can also be decent, but usually WAY overestimate the air leakage (as do many built-in defaults to Manual-J tools.) Freebie online tools such as LoadCalc can be OK if you assume it's completely air-tight (ducts too) and don't upsize from there.

It seems counter intuitive, but the smallest HVAC that actually covers the heat loss at the 99% outside design temp and heat gain at the 1% condition is going to be FAR more comfortable than than a system that's 2x oversized, and sometimes essential for comfort when the loss characteristics of different parts of the house differ, which in your case is almost certain to be the case. ASHRAE recommends drawing the line at 1.4x oversizing, but that's a maximum. There is usually more than 15% margin built in to even professional load calculation tools. My experience with LoadCalc is about 25-30%, and that's even using the most aggressive assumptions.

For a good primer on why you need to right size it see Nate Adams' blog bits:

http://www.natethehousewhisperer.com/home-comfort-101.html

http://www.natethehousewhisperer.com/hvac-101.html

http://www.natethehousewhisperer.com/hvac-102.html

Once we have a full HVAC system, we will probably keep the house heated all winter, at least to 50 degrees or so, so we do not have to winterize.

That varies quite a bit. In many areas any new construction/renovation has to be brought to current code minimums, and in any heated building HVAC systems have to be sized to cover the 99% heating load even if usually not used in the winter. Even if not fully winterizing addressing the most egregious of the shortcomings of the sub-code original part of the building makes it more comfortable, an smaller HVAC systems can be specified. If installing ducts, it is STRONGLY recommended to run them in an insulated sealed crawlspace, which is far superior to the (commonly done but totally wrong for comfort, efficiency and air quality) in a vented attic above the insulation, which increases the actual loads, and drives outdoor air infiltration.

Based on what you said, when we jack up the roof to replace the bottom plate of the wall, we should install EMD under our new plate, correct? Do we just drape that all the way down the inside of the block? We also plan on digging outside down to the garage foundation to see what we can see there and install a french drain and/or sump pump if we feel necessary...or is that overkill? I have a sump in my Columbus area house, but that has a full basement.

Yes, EPDM under the sill plate running down the side of the block is the right way to go if the block wall is substantially below grade. If it has a few feet of above grade exposure on the interior just putting it between the block an the wood will be sufficient.

 

[dankoos]

so the HVAC guy we have been talking to wants to install the furnace/unit in the crawl space under the house....this worries me due to how damp it has been down there due to the rain...while not the worst crawl space ever, I just fear air from down there will pick up mold spores and send them through the rest of the house...thoughts on this??

 

[Dana]

so the HVAC guy we have been talking to wants to install the furnace/unit in the crawl space under the house....this worries me due to how damp it has been down there due to the rain...while not the worst crawl space ever, I just fear air from down there will pick up mold spores and send them through the rest of the house...thoughts on this??

If you insulate and air seal the crawlspace walls and put down a ground vapor barrier putting the furnace in the crawlspace is nearly ideal, since it would be fully inside the thermal and pressure boundary of the house. It's only damp & disgusting down there if it's uninsulated, has no ground vapor barrier, and sucks in outdoor air from leaks/vents.

If installing a combustion appliance or heat pumps down there it's good to install a 2" rat-slab over the ground vapor barrier to avoid damaging the vapor barrier and support the equipment better.

 

[dankoos]

If you insulate and air seal the crawlspace walls and put down a ground vapor barrier putting the furnace in the crawlspace is nearly ideal, since it would be fully inside the thermal and pressure boundary of the house. It's only damp & disgusting down there if it's uninsulated, has no ground vapor barrier, and sucks in outdoor air from leaks/vents.

If installing a combustion appliance or heat pumps down there it's good to install a 2" rat-slab over the ground vapor barrier to avoid damaging the vapor barrier and support the equipment better.

I appreciate all your time responding to me. So let's talk insulating the crawl again. the crawl currently consists of block walls, concrete floor, floor joists above. There are three vents...one leads to garage (garage was added at some point after the house) and two lead outside. The two outside vents have been blocked off with plywood.

To insulate the crawl properly, especially if we do this HVAC, you are saying lay that EPDM on top of the concrete floor, and then insulate the block walls with foam, or rigid insulation? The floor joists above are currently insulated with foil faced bat insulation. would we want to have the new HVAC system blowing some air into the crawl? We would not want a return vent in the crawl, correct? Would we want to "paint" the block walls and/or concrete with drylok or similar at all?

 

[Dana]

I appreciate all your time responding to me. So let's talk insulating the crawl again. the crawl currently consists of block walls, concrete floor, floor joists above. There are three vents...one leads to garage (garage was added at some point after the house) and two lead outside. The two outside vents have been blocked off with plywood.

To insulate the crawl properly, especially if we do this HVAC, you are saying lay that EPDM on top of the concrete floor, and then insulate the block walls with foam, or rigid insulation? The floor joists above are currently insulated with foil faced bat insulation. would we want to have the new HVAC system blowing some air into the crawl? We would not want a return vent in the crawl, correct? Would we want to "paint" the block walls and/or concrete with drylok or similar at all?

Drill through the slab to see if there is already a vapor barrier in place. If the seepage moisture is just coming through at the wall and can be dealt with by a perimeter drain it may be fine to skip putting a vapor barrier over the slab.

Insulate the walls as if it were a hobbit-basement. Columbus OH is in US climate zone 5, where for the above grade section of the walls at least R5 of foam would be enough for wintertime condensation control using an R13 (kraft faced or unfaced but not foil faced) studwall. An inch of foil faced polyiso would be the preferred foam board if going with a studwall + foam option. For an all-foam option it takes R15, which would be 3" of paper or fiber faced roofing polyiso, or 2.5" of foil faced wall sheathing polyiso. Leave an air gap between the bottom edge of the foam and the slab, given the seepage history. Any foam needs to be covered with a timed thermal barrier against ignition. Half inch wallboard is fine, even if unpainted. But in the studwall + foam option paint the wall with at least a primer coat to serve as a vapor retarder.

Code requires at least 1 cfm of ventilation per 50 square feet of crawlspace floor area, which isn't much. The best way would be to install an appropriately sized Panasonic Whispergreen moving air to/from the conditioned space above in one corner of the crawlspace, and a small return grille through the floor to the conditioned space at the far corner.

Don't have the furnace actively heat the space at all- it doesn't really qualify as "ventilation", since it's only moving the air when there is a heating load, and even a small heating register would be unnecessarily dumping gobs of heat into that space when running, probably overheating it.

You'll have to pull back the foil faced batts of the crawlspace ceiling to adequately air seal an insulate the band joists, but it's otherwise fine to leave it in place.

It's best to use cut'n'cobbled foam board can-foamed into place at the top of the foundation and band joist, but as long as it's at least R5 it's fine to use care R15 rock wool (more fireproof than fiberglass) to fatten up the R-value there rather than stacking up R15 or more of foam-board:

^^^This diagram isn't enough foam for a foam-only solution, but shows what to do at the top of the foundation and band joist.

Be sure to run your own Manual-J heat load calculations for sizing the furnace, and oversize by no more than 1.4x from the 99% design load if possible. Most HVAC contractors oversize by 2x-3x or more using crummy rules of thumb. The oversizing doesn't cost much extra in equipment, but it's substantially less comfortable than right-sizing it. Often the only way to truly right-size it is with cold-climate heat pumps, which can be a great option if you are also air conditioning the place.

 

[dankoos]

Ok, I have been doing a lot of research after reading your responses. It appears that my crawl space having a concrete floor is quite rare (especially for a house built in the mid-70's). I don't want to drill through the floor in there, so I am just going to assume it needs a vapor barrier. Are you suggesting the EPDM because the floor is concrete? For dirt/gravel floors, all I see in my research is 6mil or 12 mil poly/plastic material that gets laid down and sealed with PVC tape. Regardless of the material, should it lap up the walls to the last block high before installing rigid foam insulation? Speaking of, this is what you are talking about, correct?

https://www.menards.com/main/buildi...-insulation-4-x-8/w-n5200/p-1444438919949.htm

I would just attach this to the walls using specialty screws or construction adhesive, correct? Then what, tape or foam the seams? For the rim joists, just cutting this same foam to size and shoving it in there works? That is what I see on the videos I have watched. Looks like they spray foam around the edges for tight seal. What I don't quite understand is what to do where the bottom plate of the house walls meets the block foundation walls. It appears you have to leave that open for insect/termite inspection, but won't that be leaving a gap in this new insulation/vapor system?

Lastly, it appears that once the space is insulated and vapor barrier installed, installing a permanent dehumidifier with a pump to drain the water to the outside is the best way to go to be sure the humidity level does not get above 60-70%? I have read where if you allow a little conditioned air to be fed down there that won't affect the pressure at all, but in the spring/fall the HVAC system probably won't be used a ton anyway, so the dehumidifier is a good way to be sure the air is circulating and the moisture stays out.

 

[Dana]

If you're installing 12 mil poly (6 mil isn't rugged enough for a "walkable" vapor barrier) or EPDM (membrane roofing) AND foam board, the vapor barrier only needs to come up 12-16" up the wall. It can be glued & taped to the wall prior to installing the foam board, but ends up being sandwiched/clamped between the foam board and foundation. If you are installing a furnace down there the fire ratings of the vapor barrier are goint to matter if it's on top of the slab- I'm not sure if 12 mil polyethylene would cut it, but I'm pretty sure EPDM roofing does. Run the plan by the inspectors BEFORE installing any of it.

Yes, the polyiso foam board from Menards would be fine, but reclaimed roofing foam from commercial building re-roofing/demolitions can be cheaper & better.

Do NOT use standard construction adhesives- they have solvents that will degrade the foam board. There is specially formulated foam board construction adhesives that won't affect the foam. If installing an interior side studwall or furring to trap the foam to the wall and mount the fire-resistant thermal barrier (half-inch wallboard is good) you won't need to use any cap-screws. If it's furring rather than studwall, use coated masonry screws through-screwed into the foundation.

Unless you live in a termite zone the inspection strip isn't necessary. If you DO live in a termite zone, insulate the inspection strip with carefully trimmed rock wool batt that can be removed for inspection and re-installed.

A dehumidifier works for keeping the humidity low enough and would meet IRC code under R408.3, section 2.4 , but uses quite a bit more power than a tiny blower delivering a slow-but-steady exchange with air from the rooms above. The tiny blower approach also doesn't have to deal with condensed water disposal. One of these is good for up to 500' of crawlspace floor area and draws just a hair more than 2 watts. Even with a small amount of ducting and a couple of tiny floor registers you're looking at less than $200 total cash outlay. A code-minimum 70 liter dehumidifier solution draws more than 500 watts, and even operating under a low duty cycle is chewing more power, costs more up front, and has a shorter lifespan.

 

[dankoos]

Again, thank you for the quick response! One last thing...the research I have done recommends taking down the bat insulation inbetween the floor joists...you mentioned I could keep it in. I think I plan on taking those down as I am guessing they are not helping with the mildew smell and some have fallen already anyway. I don't know for certain, but guessing there is some mold on those joists in spots...is it worth it to have them sprayed with something or have it professionally removed if there is any? Also, the water line comes into the crawl in I believe two different spots (which is weird to me, but it appears that way, the main meter is outside in the front yard in a sump it with a lid), what is best way to seal that entry point? I believe there is some sort of cleanout coming in through the block as well. I can take pics this week and post them if it helps. Actually, below is a link to some pics I took before we bought the place (this also includes a few photos of that garage wall):

https://photos.app.goo.gl/xDywnqNqAs3YeRFd6

 

[Dana]

Again, thank you for the quick response! One last thing...the research I have done recommends taking down the bat insulation inbetween the floor joists...you mentioned I could keep it in. I think I plan on taking those down as I am guessing they are not helping with the mildew smell and some have fallen already anyway. I don't know for certain, but guessing there is some mold on those joists in spots...is it worth it to have them sprayed with something or have it professionally removed if there is any? Also, the water line comes into the crawl in I believe two different spots (which is weird to me, but it appears that way, the main meter is outside in the front yard in a sump it with a lid), what is best way to seal that entry point? I believe there is some sort of cleanout coming in through the block as well. I can take pics this week and post them if it helps. Actually, below is a link to some pics I took before we bought the place (this also includes a few photos of that garage wall):

https://photos.app.goo.gl/xDywnqNqAs3YeRFd6

It's fine to take down the ratty batts even though it wouldn't be absolutely necessary. If there is going to be a furnace and ducts down there the batting isolates the fully conditioned space from the distribution losses to the crawlspace. If the plan is to go with fully insulated exterior walls it won't make much difference in energy use either way- there is no good reason to keep them, so by all means, yard 'em on out.

The frame walls appear to have asphalted fiberboard sheathing on exterior, not plywood. It also appears that the sill plates resting on the foundation have a bit more oxidation or mold on it. Asphalted fiberboard is fairly moisture tolerant, but also vapor permeable. If the house is going to be air conditioned it's important keep the interior side reasonably vapor permeable as well or summertime moisture could collect in the wallboard. Standard latex paint is fine, foil wallpaper is not. Polyethylene vapor barriers would risk condensation collecting on the vapor barrier and insulation, potentially leading to rot on the stud edges.