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No vent at each rafter bay . How to solve venting issue attic

No vent at each rafter bay . How to solve venting issue attic


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Old 07-17-18, 02:14 PM
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No vent at each rafter bay . How to solve venting issue attic

House was built late 50's . Each rafter bay in attic does not have a vent . How should I solve this venting issue ?? (I will be adding more blow in )
 
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Old 07-17-18, 02:21 PM
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You don't generally vent EVERY rafter bay.
 
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Old 07-17-18, 02:28 PM
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Isn't that how new houses are ?
 
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Old 07-17-18, 02:30 PM
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Not the ones around here. Probably depends on your climate.
 
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Old 07-17-18, 02:34 PM
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That's how they are in zone 2 for the past 20 years or so
 
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Old 07-17-18, 02:56 PM
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A house built in the late 50s is not going to have raised heel trusses (often referred to as an energy truss). Modern houses with that type of truss might ventilate every rafter because they can do that and still maintain plenty of insulation above the exterior wall.

if you choose to ventilate every rafter on a 1950s home that simply has birdmouthed 2x4 or 2x6 rafters sitting right on top of your exterior wall, you are sacrificing insulation for ventilation. You will have increased heat loss (directly above the top plate) and a cold ceiling perimeter as a result.

You can put stryrofoam chutes in every rafter bay if you want, but know what you are sacrificing as a result. Increased heat loss from the house perimeter can aggravate ice dams come winter. If you feel that will be offset by your added insulation, go ahead. But the traditional way to ventilate a house from that era is probably the way it is currently being vented... with measured ventilation every 4-8 ft or so.

Bud is our resident expert on this topic, he will probably be along to comment shortly, so stay tuned.
 
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Old 07-17-18, 03:03 PM
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I ll try to get pics to show what type of truss it is . But I am personally unable to climb in there .

can u post pics of the difference truss so I can figure out what type I have!?! (Exterior has vented soffits but that could of just been replaced at some point even tho there wasn't vents . )

if it is vented every 4 to 8 feet. What's the proper way to add more blown in installation and how much for my zone . Etc .
 
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Old 07-17-18, 03:09 PM
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Houses that old will usually be stick built and will have rafters, not trusses.
For pics, just Google the word truss. Or raised heel. Then click on images.

To add blow in while still keeping those individual bays open, you would insert a styrofoam chute out into the soffit so that it is slightly past the top plate, then you stuff insulation between the chute and top plate to block insulation from entering the soffit. The chutes are about 4 ft long that that allows you to add lots of insulation.
 
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Old 07-17-18, 03:58 PM
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So what do I do differently if I have truss'?
 
  #10  
Old 07-17-18, 04:05 PM
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Hi wantboost,
The objective is to provide sufficient NFA (net free area) both low and high so that natural air flow will remove warm air and any moisture it is carrying. I summer it will help a little by removing some of the heat.

Having vents every 4 feet will make it difficult to reach the total NFA you want, plus the soffits should be open internally so that air entering one vent can flow to all others. The baffles that X suggested are necessary to prevent the new blown-in insulation from blocking the air flow below the roof deck as well as keeping it out of the soffits.

Yes, getting the baffles down into the lower areas is a pain, but necessary. Basically the insulation will hold them in place, no need to get fancy. I've installed some with just two staples at the top and once the insulation is in place they are there for good. The fold of insulation at the bottom that X suggested holds the lower end in place.

Bud
 
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Old 07-17-18, 04:21 PM
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I ll check what type of roof I have . Is there any measurements I need to do for u guys ?

With the baffle sitting on fiberglass insulation will that still allow for air flow ? (which way should the fiberglass bat sit? Vertically or horizontally so it breathes better .... I assume it's just there as a blocker for the blown in not to fall in the soffits ? )
is the batting still needed on rafter style?
 
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Old 07-17-18, 04:32 PM
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Old 07-17-18, 06:24 PM
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This is a soffit constructed with a birdsmouth cut in a 2x6 rafter resting directly on top of a double plate.
https://www.google.com/search?q=how+...bWXpmJPBVfYCM:
As you can see there is minimal space above the top of the wall and you need to fit some insulation in there.

With a raised heel truss they essentially extend the wall upward before they attach the rafter which allows more space for insulation. I doubt your home has this feature. Most likely the first link above.
https://www.google.com/search?q=rais...a4D9FZX3w1OAM:

But that is standard construction for a 50's home.

Bud
 
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Old 07-18-18, 05:58 PM
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Best pic I have currently. I can get more if need be

 
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Old 07-18-18, 06:24 PM
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The roof deck in the back left area sure looks dark, which is often an indication of a moisture problem.

You do not have trusses just standard rafters and looks like a hip roof, slope from ends as well as sides.

Bud
 
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Old 07-18-18, 06:28 PM
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I ll get more pics .
do I have low vents ?
and how many high vents should I have?
how much insulation should I add .
 
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Old 07-20-18, 07:57 AM
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Need more information and perhaps a couple of outside pictures to determine if you have a location for low vents. In the 50's they were not very concerned about ventilation or insulation. Check local code requirements but i would assume r-50 or close to it for the ceiling (attic floor).

Guidance for ventilation would be 1 ft² of NFA (net free area) for every 150 sq ft of attic floor. Half of that number goes to the high area and the other half to the low source.

Do you have a ridge vent or other high vents?

Do you have soffit vents?

Bud
 
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Old 07-25-18, 03:51 PM
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Got a quote today for top up.
I have 5 roof vents and he says theres about a low vent every 10 to 12 feet .
house is about 1200 sqft
so is this adequate?
 
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Old 07-25-18, 04:07 PM
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At 1,200 ft² the normal guidance for your age home is 1 ft² of NFA (net free area) for every 150 ft² of attic floor. Dividing 1200 by 150 gives you 8 ft² of total NFA for high and low. Divide that equally and you need 4 ft² for high and 4 ft² for low.

Your next task is identifying how much NFA your current vents are providing. With pictures we can help guess.

IMO, the person who gave you the quote should have provided this information.

Bud
 
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Old 07-25-18, 04:12 PM
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I still should tell them to put fiberglass at each vent so blown in doesnt fall into sofit?

heres a pic . One vent isn't shown in pic cause it's on other side if house .
Even in the past with Insulation companies they have no idea that there is a formula/different style rafters etc etc . No one even knows about putting fiberglass batting at vent . They just wanna cash in

 
  #21  
Old 07-25-18, 04:31 PM
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Looks like you are ok for high vents but I can't see the low vents in the soffit. However, I suspect there is not enough low vent area. So two questions.
1. can you take a picture of the vents in the soffit from below them, not from the attic.
2. From that picture or if you can tell me, is the space above the soffit open such that air entering the existing soffit vents can flow to any rafter bay.

Bud
 
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Old 07-25-18, 04:34 PM
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Soffits are all perforated . But suppsueeldy only cut out every 10 to 12 feet

 
  #23  
Old 07-25-18, 04:43 PM
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The vinyl can be removed to expose whatever is up there for soffits. For the current insulation work there should be baffles in EVERY rafter bay and a fold of batt insulation stuff near the bottom to block the new blown in insulation from filling the soffits. be sure the fold of fiberglass insulation doesn't crush the baffles or block the air flow from soffit to ridge above the baffle.

Bud
 
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Old 07-25-18, 04:47 PM
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They are only putting baffles at rafter bays that have a vent cut out .
 
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Old 07-25-18, 05:52 PM
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"They are only putting baffles at rafter bays that have a vent cut out . " I know you said that but I'm saying that is wrong. Ventilation needs to remove moisture below the entire roof deck. During cold weather moisture vapor makes its way right through the ceiling assembly up to that cold roof where it will form condensation and rot out the roof.
 
 

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