Replies

1. 
   DanH | Jun 01, 2012 09:31pm | #1

   Most formulas work from square feet of roof.

1. 
   cameraman | Jun 02, 2012 01:56pm | #2

   Photos

   I am in the process of reroofing our house, which has only 2 small roof vents and no soffit vents.

   I plan on cutting in soffit vents adding roof venting. In process of figuring out how much and were.

   I will only have about 15' of ridge vent, total.

   Where and what type of roof vents would I need?

   Would I calculate venting by SQ ft of floor space in the attic or just vent all that I can on this type of roof?

   
1. 
   JimB | Jun 02, 2012 03:32pm | #3

   I thought that I had posted this earlier, but here's some

   information that will help.  Note that you need to determine the net free vent area for each vent product.  That is usually stamped on the vent or shown on the packaging.

   http://www.ashireporter.org/articles/articles.aspx?id=1889

2. 
   calvin | Jun 02, 2012 04:14pm | #4

   Most formulas work from square feet of roof.

   or square feet under roof?

2. 
   NicholsConstruction | Jun 03, 2012 09:58am | #5

   I believe a general rule of thumb for venting attics is to have at least 1 sq" of ventilation,(net) for every 1 sq'  of attic area, and about half of that if your ventilation is balanced pretty evenly between soffit and ridge.  If you do not have enough lin ft of ridge to meet these minimums, then you may want to consider venting your hips with something that is very much like a shingle-over ridge vent.

   Len

1. 
   DanH | Jun 03, 2012 10:51am | #6

   I'm thinking that most codes require something less than the inch per foot, but it's still a fair "target".

   In the OP's case, with the relatively small hip with eaves on all edges, the eaves become a substantial fraction of the overall roof area, and one might wonder if the eaves should be counted in the "area of the attic" which is generally the base number used.  Probably so if they were enclosed, but they aren't.  Of course, since they aren't enclosed achieving good eave venting will be a challenge.

   Basically, with this roof, one would probably just do the best they could with both ridge and eave venting, trying to achieve a modicum of "balance" between the two (no more than maybe a 3:1 ratio one way or the other).  The sort of slanting ridge vent intended for hips is a good thing to look at.  For the eaves there are several options, but it depends on the details of construction.

3. 
   cameraman | Jun 03, 2012 03:13pm | #7

   Venting

   I will measure up my attic sq ft and get back.

   The soffets open unrestricted into the attic, so cutting screened vents should be no problem.

   I have seen the slanted ridge vents on roofs. Will check that out.

   Concerned that adding a static type vent in addition to the ridge vent will not give the results that I need.

   thanks

1. 
   cameraman | Jun 03, 2012 03:34pm | #8

   hip roof ridge vents

   http://www.airvent.com/professional/products/ridgeVents-hipridge.shtmlhttp://www.airvent.com/professional/products/ridgeVents-hipridge.shtmlhttp://www.airvent.com/professional/products/ridgeVents-hipridge.shtml

   Would this be a product to use on the hip roof ridge vent.

1. 
   DanH | Jun 03, 2012 05:49pm | #9

   Only after you delete the two extra copies of the URL.

4. 
   oops | Jun 03, 2012 08:08pm | #10

   venting attic

   Min. area requied. Total net free ventilating area shall not be less than 1/150 of the area of the space ventilated except that the total area may be reduced to 1/300 provided that at least 50% and not more than 80% of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet above the eave/cornice vents with the balance of the required ventilation proviede be eave/cornice vents.

   There is more, but this is pretty much answers you question. Roughly per International Residential Building Code.

1. 
   DanH | Jun 03, 2012 08:31pm | #11

   Of course, since this is a retrofit there's no requirement to meet the current code (unless there are other major upgrades being made).  More just a "best effort" sort of thing.

5. 
   IdahoDon | Jun 03, 2012 11:13pm | #12

   I think this has been covered about 100 times before.  Basic questions like this are pretty easy to answer if you just search the past topics.

6. 
   cameraman | Jun 05, 2012 07:50am | #13

   Venting

   I am assuming I need it, it is ungoldly hot in the summer time. No signs of mold, just thougth it would help cool down the attic and 2nd floor.

   Plan is also more insulation in the attic after I finish the roof,

   Thanks to all for input, I guess I did get lazy and should have searched the forum first.

   Thanks again, Lots of idea's and comments.

7. 
   GriffithSykesse | Jun 21, 2012 06:17am | #14

   The sort of slanting ridge vent intended for hips is a good thing to look at.  For the eaves there are several options, but it depends on the details of construction.