Cape Cod attic ventilation

Reply

  #1  
Old 03-05-19, 01:55 PM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Cape Cod attic ventilation

I've got a minor mold/moisture situation in my attic, and I could use some advice as to how to handle it. A little back-story: I live in a Cape Cod style house just outside of Chicago. About two years ago I renovated the two upstairs bedrooms for my kids. Part of the work included removing the drywall and wood paneling at the knee-walls and exterior walls to reinsulate between the 2x4 framing. Previously, there was very thin foil-faced insulation in those walls. The same insulation was found between the rafters in the knee-wall space/low portion of the roof, which I removed entirely. The sloped ceiling/roof had 5.5" or 6" kraft-faced batts already installed (R-21, if memory serves). I chose to leave those batts, since they seemed more than adequate, and it also allowed me to leave the drywall/paneling in place on the sloped/flat ceilings - which I then drywalled over. The floors in both the knee wall space and upper attic have 3.5" faced batts w/ blown in fiberglass insulation on top. Those areas were also left mostly untouched, other than to tidy up or ensure voids were filled.

I can't say that during the course of the work I didn't see any signs of moisture on the decking/framing, but due to the fact that it wasn't yet heating season, the decking/framing was relatively dry. Shortly after finishing, I went up in the attic thru a drywall access in an unfinished storage space the previous owner had created, and found a fair amount of moisture, rusted roofing nails, mold, etc. Pretty typical for the posts I've read on this forum about Cape Cods. At the time, I determined that there was insufficient venting between the lower attics and upper attic - whoever installed the 6" batts nailed two strips of ~1.5" lattice in a V-shape between the decking and insulation, which left maybe 1/2" for air to travel on a good day. Since the spaces were finished and being used, I decided to pull the lattice and scew 2" PVC sections at each rafter bay to the underside of the deck as sort of a retrofit option. I did most of the work thru the lower attic spaces. I also went into the upper attic and sealed around any junction boxes, conduit penetrations, etc. I assumed this would solve my problems.

I climbed up in the upper attic about a week ago to check on things, and the problems had resurfaced (albeit to a lesser extent). The lower/knee-wall spaces are sealed, but the problems in there were relatively minor compared to the upper attic when they were originally discovered.

My questions are a) is the 2" PVC adequate for ventilation between the attic spaces b) are there enough roof vents (currently 4, I assume 50-60 NFA) c) are there enough soffit vents (number/size unknown due to sheet metal soffits installed by previous owner - there are vented sections, but hard to tell if they're all open) and d) what else am I missing here?

A couple other pertinent bits of info:

Approximate building footprint under the roof is 1140 SF.

A whole house humidifier was installed after we moved in, due to frequent dry skin problems and nose bleeds. I try to maintain humidity levels per the chart on the humidistat.

Let me know if more info is needed. I'd appreciate any tips/advice I can get.
 
  #2  
Old 03-05-19, 03:20 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Ventilation between the lower attic space and the upper is more than just a path. It needs to wash below the roof deck to cool and remove moisture, although you can't see what is happening in there. Guidance looks for a 2" gap between insulation and the roof (minimum of 1"). And yes the 5.5" rafters aren't providing all the space you would like. A quick search indicated about R-40 which I won't get into the "how to" as I doubt you are going to try.

1200 sq ft on an existing home would need 8 ft² of NFA (net free area), half assigned to the high vents and half to the low. If we use 4 high vents at 60 in² each we get 240 in ² where we need 4x144 = 576. So we are a bit short, but it will work if we have reasonable low venting. Does your cape have matching front and rear sloping roof lines or is there a dust pan (shed dormer) off the back?

For now the issue points to low vent area, to be determined, and more searching for leaks from house to attics.

Note: Air leakage from house to attic would be more of a problem with more humidity. What is your target for the humidifier?

Another note, a house that is experiencing dry air is also experiencing excess air leakage, by definition. A very well sealed home may actually require a dehumidifier during the winter as moisture produced by the occupants and their normal activities is more than a home needs.

For now
Bud
 
  #3  
Old 03-05-19, 05:31 PM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Bud, thank you for your quick reply.

The house is cross-gabled (like an L), with a very small shed dormer for a bathroom on the backside.

If the rule of thumb says I need 576 in ², shouldn't I be adding vents along the roofline (or gable vents)? I believe the soffits are plywood w/ aluminum panels over them. Would you recommend removing the panels and cutting in openings in the plywood as needed? Do aluminum soffit panels inhibit ventilation?

As for the humidity, I typically keep it under 35%. The last couple days have been around 10 degrees, so we're down below 25% right now. Generally, if I see the old wood windows start to fog up, I know I need to go turn it down. We've become less reliant on the humidifier as our family has grown.

I've never had an energy audit done or anything like that, but I would guess that the house is fairly drafty - all the doors and windows are original to the home.
 
  #4  
Old 03-05-19, 06:24 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
I assume the aluminum soffit panels are perforated but yes they reduce the NFA, I usually estimate 50%. But we don't know what size openings are under them.
You could tru running a few really bright lights up into the attic to light it up. And then at night take a look at the soffits from outside to see what you can see. Might give you an idea as to how many holes are there and where they are located.

Now, if current ventilation isn't solving the moisture problem it most likely is not entirely a ventilation issue. The guidelines they push so hard actually have a plus or minus tolerance. Are you ready, plus or minus 80%. That is actually my number, as no one has ever put a working tolerance on ventilation and unfortunately it leaves home owners shooting, at some expense, to hit exactly the calculated number, which is BS. I have the details to support my wild accusations, but for now just accept that any amount of ventilation is usually good.

Now for the source of that moisture which is where I think we need to focus. Some pictures of that attic and perhaps an outside shot or two.

When there is a significant air leak into an attic there is often an indication of mold directly above it. Check for disconnected bath or kitchen fans and be sure they are vented to the outside and not to the soffits. Drop ceilings like above kitchen cabinets and sometimes stairways can be a source of air. Around chimneys and plumbing vents as well.

What do you have for a basement, concrete floor, finished or not?

The small shed dormer you mentioned, does it have soffit vents as well?

I'll wait for pictures tomorrow.

Bud
 
  #5  
Old 03-05-19, 08:02 PM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
I'll work on getting photos of the attic space as soon as I can, but I might not be able to get to it tomorrow. It's a bit of a cramped space, and the access opening is tight, so it's a minor ordeal to get up there. Is there anything in particular you'd like me to focus on?

Right now, I don't have access to the lower attic spaces. I intended to put an access door in a closet to give me access to the main area, but I never got around to it. This would obviously make it difficult to light up the soffits. I'm certainly willing to open up the drywall if necessary.

There is a first floor bathroom fan in a plaster ceiling that I suspect vents into the soffit. Without opening up the ceiling, I assume the next best place to check is outside by removing a portion of the soffit.

We have a full basement, with a concrete floor. The previous owner painted the slab, and foundation walls, and there is a finished drywall ceiling. I don't know if I'd call it a finished basement. I believe there is a drain tile around the perimeter of the house - there is a sump pit with a pipe that extends towards the foundation wall.

The shed dormer has a small eave (12"), but the soffit panels are not perforated. I took a walk around the house to see where I saw perforated panels - I see a total of 6, but again, sizes are unconfirmed. As an aside, how much would it matter where the soffit vents are placed? There is an area at the inside part of the "L" that is typically much more damp than the other areas whenever I've observed problems in the upper attic. There are no perforated soffit panels on this section, and I suspect that there is very little airflow there.

I really appreciate your input so far, thanks again.
 
  #6  
Old 03-05-19, 10:27 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
"Is there anything in particular you'd like me to focus on?"
Any area where you see/saw moisture, the bottom of the roof and the insulation below.

The eaves where the insulation may be blocking the air flow.

The opening on the inside for one of the high vents. If you can see check to see if the bug screen is clear or blocked. From the outside (if you can see) be sure the vents are not buried in snow.

The bottom of the roof in that dust pan area.

Any areas you can see over the ceiling fans or around vent pipes.

I feel your pain, I'm too old (and too fat) to be going up into my small attic, I live in a cape and I'm claustrophobic. Last trip I had to just lay there for awhile to get my heart rate to calm down.

Do you have boards or plywood up there to walk on?

Bud
 
  #7  
Old 03-06-19, 07:54 PM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Bud, I took some photos tonight, but there are a few too many to post here. Not sure how else to give you the whole picture, and even so, they're all probably pretty confusing. It's a physical challenge to climb around on the ceiling joists in that cramped space! Please let me know if you have questions. I tried to label the photos accordingly. The link is below:

https://imgur.com/a/8MaMifm

They were all taken from the upper attic. As I said before, I don't have access to the lower attics right now. I can open up the drywall if need be, but probably not until the weekend. I can tell you that the rafters above the soffits were clear last time I was in there.

We had a couple sub-10 degree days this week, so you can see the decking/rafters in some areas, particularly near the east gable, were very damp.

Thanks again.
 
  #8  
Old 03-06-19, 08:19 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Pictures do help a lot and, hate to say, you have a real mess up there and i have no idea as to how to advise cleaning that up. I'm done for the night anyway so will rethink tomorrow and maybe some of the pros will jump in and add advice.

I think the rafter bays that are wet are clearly lacking airflow from below, be it the pvc pipe, insufficient soffit vents, or lack of baffles.

I'll be back.

Bud
 
  #9  
Old 03-07-19, 04:16 AM
S
Member
Join Date: May 2006
Location: upstate New York
Posts: 402
Received 0 Votes on 0 Posts
ventilation

I'm no expert, but in post #5 you mention a bathroom exhaust fan. I'd be making sure that fan exhausts OUTSIDE. Steve
 
  #10  
Old 03-07-19, 06:03 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
I do some of my best thinking just before I fall asleep, even keep a pad of paper there to make quick notes so the thoughts aren't lost come morning.

Up to you to decide how aggressive you want to get at cleaning up that attic space and I have not seen the lower space, is it similar?

The moisture up there is continuing to damage the roof deck and the mold is spreading so drying it out ASAP is a high priority. A fan could help if you have a place to blow out attic air. Even just circulating air will help.

The cavities between the lower and upper attics where we see the pvc pipes need a space between the roof deck and the insulation. We are assuming the soffits have good airflow. I hate using anything combustible to generate smoke but a search for smoke generators to test air leaks and ventilation will turn up some train smoke devices that aren't too expensive. They may have other options as well.

You mentioned removing some drywall to ger better access, a really good idea as much work will need to be done. Kind of long term temporary access openings that you can open and close on a day to day basis.

One picture shows a gable end with a few holes drilled in the rafters, where is that and what is on the other side?

Spring is coming .

Bud
 
  #11  
Old 03-07-19, 08:03 AM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
"I'm no expert, but in post #5 you mention a bathroom exhaust fan. I'd be making sure that fan exhausts OUTSIDE."

Steve, you are correct. That's probably Item #1 on the list now, since it'll probably be the easiest thing to rectify. I plan to open up the soffit this weekend to find and reroute the flexible duct, weather permitting.
 
  #12  
Old 03-07-19, 08:22 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
We don't have a "like button" so I'll say thanks here Steve.

If the bath exhaust fan is dumping into the attic that could be a major contributor, even when not running. The dampers in exhaust fans open on outflow and often provide a 24/7 path into the attic. Be sure all exhaust fans are vented to outside.

Finding a place to reroute that vent can be difficult, a side or end wall is best. Dumping warm air out a soffit isn't the best, but when it is the only choice they make vents that direct the exhaust down and away from the house.

Bud
 
  #13  
Old 03-07-19, 08:24 AM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
"Up to you to decide how aggressive you want to get at cleaning up that attic space and I have not seen the lower space, is it similar?"

When I originally uncovered these issues a couple years ago, the lower attic spaces were in much better shape than the upper attic. I'm not interested in putting a bandaid over anything - I want to get it right and move on.

"The moisture up there is continuing to damage the roof deck and the mold is spreading so drying it out ASAP is a high priority. A fan could help if you have a place to blow out attic air. Even just circulating air will help."

I'll see what I can do about placing a fan or two up there.

"The cavities between the lower and upper attics where we see the pvc pipes need a space between the roof deck and the insulation."

This much is understood. I plan to open up the sloped ceilings to correct this. My initial thought is to remove the existing insulation, furr out the rafters w/ 2x2s, install baffles and new insulation. Do you have another suggestion?

"We are assuming the soffits have good airflow. I hate using anything combustible to generate smoke but a search for smoke generators to test air leaks and ventilation will turn up some train smoke devices that aren't too expensive. They may have other options as well."

Are you suggesting I do this to check for airflow between the soffits, lower, and upper attic spaces, or just as a general assessment between the living spaces and attics? If it's the latter, I'm considering hiring an energy auditor to come in and check the whole house. Your previous comment about drafty homes needing humidifiers has me thinking.

"You mentioned removing some drywall to ger better access, a really good idea as much work will need to be done. Kind of long term temporary access openings that you can open and close on a day to day basis."

I agree, there's really no way around it. Unfortunately, that means opening up three separate spaces.

"One picture shows a gable end with a few holes drilled in the rafters, where is that and what is on the other side?"

This is on the east side, where the worst of the photos were taken. I believe it's just an empty eave on the other side of the rafters. Not sure if it's noteworthy, but there are no perforated soffit panels on any of the gable ends.

Truly appreciate your help so far, and thanks for not giving up on me after seeing the photos!
 
  #14  
Old 03-07-19, 08:50 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
"This much is understood. I plan to open up the sloped ceilings to correct this. My initial thought is to remove the existing insulation, furr out the rafters w/ 2x2s, install baffles and new insulation. Do you have another suggestion?"

Access to work is the key. Spacers on both sides and a baffle of some type below is good. When it can't be installed I've slid it a pre-made baffle with spacers and tacked it in place. Then stuffed some batt insulation under it to hold it up and in place.

"Are you suggesting I do this to check for airflow between the soffits, lower, and upper attic spaces," Yes, but a fog generator can be used in many places.

"and thanks for not giving up on me after seeing the photos!" I was having an anxiety attack looking at that tight attic. But thank you for wanting to fix it right. It is tough when a home owner is looking to flip a fix and just wants to hide as much as possible. DIY is an opportunity to DIR (Do It Right).

Bud
 
  #15  
Old 03-07-19, 09:27 AM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
"Access to work is the key. Spacers on both sides and a baffle of some type below is good. When it can't be installed I've slid it a pre-made baffle with spacers and tacked it in place. Then stuffed some batt insulation under it to hold it up and in place."

If I open up the sloped ceilings, I should have plenty of space to work. It would be far too difficult to try to retrofit anything from either the upper or lower attic spaces. I know that already from the failed PVC experiment. Do you have any opinion one way or another on the plastic/polystyrene vent chutes they sell at the big box stores?

How concerned should I be about the amount of insulation in the attic spaces? If you see from the photos, there are batts between the 2 x 4 ceiling joists, with 4-6" of loose fill on top. If I recall, the lower spaces are the same configuration, though the floor framing is either 6" or 8". I doubt I'm at or near what's "required", but is it sufficient? I doubt I'd be able to get much more than R20 on the slopes, unless I REALLY rework that framing. (Alternatively, would it be cost effective to use a couple layers of extruded polystyrene instead of batts?)

"I was having an anxiety attack looking at that tight attic. But thank you for wanting to fix it right. It is tough when a home owner is looking to flip a fix and just wants to hide as much as possible. DIY is an opportunity to DIR (Do It Right)."

It's no fun going up there, and I'm kicking myself for not seeing the problems when I was working on renovating the rooms, but there's no question that these issues need to be corrected.

Thanks again for all your input so far, and I apologize for all the complexities of this one. I tried to fix it once on my own, but obviously I needed some help from someone with more knowledge in building science.
 
  #16  
Old 03-07-19, 10:01 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
"Do you have any opinion one way or another on the plastic/polystyrene vent chutes they sell at the big box stores?"
2" is what we want but will never get it when space is limited 1" or 1.5" foam blocks fastened to each side with a full width pieces of rigid foam board will provide more vent area than the box store vents. Box store vents tend to not be full width. You can also cover the bottom end of the insulation to eliminate any air flowing the full length below the baffle as well as above.

If you can get r-20 that would pretty good, not code minimum but would keep the rooms up there warm. A block below the kneewall to prevent air circulation below that room is important. If you could add 1" of rigid over the inside of the rafters it would reduce the thermal bridging which cuts into the overall insulation value.

It is definitely a new age with the internet, videos, and forums like this and will only get better with time. Most of my experience was the old school of learning from my mistakes, which does have a value.

Bud
 
  #17  
Old 03-07-19, 10:49 AM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
"2" is what we want but will never get it when space is limited 1" or 1.5" foam blocks fastened to each side with a full width pieces of rigid foam board will provide more vent area than the box store vents. Box store vents tend to not be full width. You can also cover the bottom end of the insulation to eliminate any air flowing the full length below the baffle as well as above.

If you can get r-20 that would pretty good, not code minimum but would keep the rooms up there warm. A block below the kneewall to prevent air circulation below that room is important. If you could add 1" of rigid over the inside of the rafters it would reduce the thermal bridging which cuts into the overall insulation value."

Correct me if I'm wrong, but if I furr the rafters out to 7" and use the foam blocks you mention above, I can give myself 1.5" vent space, followed by 2" extruded polystyrene (R-10), 3.5" batts (R-13), and 1" extruded polystyrene (R-5) directly to the framing. That would get me to R-28 with adequate ventilation, right? Would the batts need to be unfaced if I'm using board insulation inside? Drywall directly over the 1" boards?

Below the kneewalls, the previous owner ran faced insulation in the floor joists of the attic space, then sort of rolled it up and stapled it to the subfloor and floor joists. I assume that is insufficient, since there is no real seal around the perimeter.
 
  #18  
Old 03-07-19, 10:57 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Unfaced would be my choice plus I would choose Roxul, fits tight, very dense, and a little more r-value.

With the side attics being cold that air will work its way through any fg type of insulation and form a convective loop cooling the floors of that room. what you describe sound better than leaving it open but if possible to get something in there that will block all air flow, better.

Bud
 
  #19  
Old 03-07-19, 11:21 AM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Thanks again for all your help, Bud. I'm going to get started on this at some point soon. I'm also going to do some investigating of the soffits to ensure that there is adequate ventilation there, possibly adding some vents there and on the roof and/or gables as well. First thing is getting that first floor bathroom fan routed OUT of the soffit.
 
  #20  
Old 03-11-19, 09:47 AM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Bud, based on some of your comments, it sounds like you have some experience retrofitting board insulation in a sloped ceiling, so I wanted to pick your brain one more time. Nobody in my house (the wife) is all that eager to displace the kids for any extended period of time, and obviously tearing out the sloped ceilings, framing, insulating, and putting everything back together wouldn't be a one-weekend project - probably more like 3 or 4 when you consider all the finishing work.

I'm considering working from lower attic spaces and pulling the existing batts out, and replacing them with 4" total of board insulation, which would give me an R-20. I'd be losing some R-value compared to what I had originally planned, but the upside would be the kids can stay put and the finished side of the rooms would go untouched. If you've done something similar before - how difficult was it to get the old batt insulation out, and were you able to get the board insulation to fit tightly and in position without breaking it?

Thanks in advance!
 
  #21  
Old 03-11-19, 10:18 AM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
I have little data on this approach and actually have two sloped ceilings where I will be doing this, one is half done. The approach is to simply install the desired rigid directly over the existing drywall. I'll add a link but most of that discussion deals with exterior walls and their concern relates to having an interior vapor barrier behind the drywall. I don't so my assembly will dry to the exterior. I'm obviously wanting to avoid removing the existing drywall which is no big deal for me but I like testing different options. This is a common problem with slopped ceilings not being deep enough and home owners not wanting to rip it all apart. Here is the link.

As for installing rigid into those cavities the people becomes sealing the sides of the rigid. In an open cavity you would install the rigid and then caulk or foam the sides.

Bud
 
  #22  
Old 03-11-19, 02:35 PM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Bud, if I install the rigid boards in the rafter cavities without any sealant, would you think I am opening myself up to any additional problems?
 
  #23  
Old 03-11-19, 02:47 PM
B
Member
Join Date: Oct 2008
Location: New England
Posts: 10,523
Received 37 Votes on 34 Posts
Spaced away from the roof deck they would be forming an air chute which would be fine without sealing to the sides, but it would not perform as well as an extra layer of insulation. So no additional problems just not the full benefit of the added layer. Which sounds ok.

Bud
 
  #24  
Old 03-13-19, 07:46 PM
M
Member
Thread Starter
Join Date: Nov 2012
Location: USA
Posts: 32
Received 0 Votes on 0 Posts
Thanks again!

Going to think on this and take care of some of the other problems up there first to buy me some more time.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: