Thread: Is soffit venting nessasary on slate roofs?

I*was*inspecting*a*house*recently*with*a*slate*roo f*(not*original)*and*there*was*no*soffit*venting.* The*house*was*early*1920's,*I*know*this*may*have*b een*the*standard*of*practice*at*the*time*however*w ould*you*say*this*is*going*to*decrease*the*longevi ty*of*the*roof*seeing*how*there*is*a*membrane*betw een*the*slate*roofing*and*sheathing?

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Your post is showing "*" between words.

No, soffit venting should not make a difference to a slate roof, but venting would be beneficial in keeping the attic space cooler.

Slate roofs should be installed on purlins which would allow ventilation up under the slate. Are you sure they put the slate directly on solid decking?

slates should be placed flat on the roof sheathing,with the appropriate underlayment.The slates would easily break when someone walked on the roof if installed on wood strips similar to tile roofing.Purlins are structural supports for rafters installed perpendicular to the rafters.

Originally Posted by Michael Garrity

Purlins are structural supports for rafters installed perpendicular to the rafters.

Purlins are (at least) two things:

1) supports under rafters used to reduce the span of rafters
2) supports over rafters on which roofing, typically metal roofing panels, is installed

Purlins in relation to roof structure mean only one thing.Support for the rafter

getting back to the point of the post. Lack of soffitt venting would have an affect on the roofing underlayment more so than the shingles (slate) due to condensation. But typically the older homes with slate roofs also had minimal insulation, which is a type of ventilation in itself, and tounge in groove pine underlayment, which holds up well to lack of ventilation. Example, your typical cape style home.
You should indicate lack of venting at soffits because it's not there and should look for signs of condensation in the attic and note that also if you see it.
Lack of ventilation would not cause the slate to deteriorate.

Originally Posted by Jerry Peck

Purlins are (at least) two things:

1) supports under rafters used to reduce the span of rafters
2) supports over rafters on which roofing, typically metal roofing panels, is installed

JP: I must, to an extent, disagree with definition 2. I believe, at least in my experience and in my area of the country, that the term "purlin" in only used in this fashion as regards commercial or industrial roofing applications. In my 34 years on the job I have never heard the term applied like this to residential construction. In all instances the term "lath" is substituted for "purlin".

Originally Posted by Michael Garrity

Purlins in relation to roof structure mean only one thing.Support for the rafter

Incorrect as current construction methods are.

Purlins were laid across beam to support rafters which were installed on top of the purlins - the purlins spanned from beam to beam.

Today purlins are used for two uses:
1) under rafters to support the rafters and reduce their effective span
2) across the top of rafters/trusses (which, by the way, is THE ORIGINAL USE) to support roofing systems.

Greek Architecture and American Buildings

Architectural Terms

Architectural Terms and Definitions

File:Under-purlins.png - Wikipedia, the free encyclopedia

File:Cee-portal.jpg - Wikipedia, the free encyclopedia

THIS is what you are thinking of: (in Figure 26.37)
Architectural Drafting & Design - Google Books

Originally Posted by Jerry Peck

Incorrect as current construction methods are.

Purlins were laid across beam to support rafters which were installed on top of the purlins - the purlins spanned from beam to beam.

Today purlins are used for two uses:
1) under rafters to support the rafters and reduce their effective span
2) across the top of rafter trusses (which, by the way, is THE ORIGINAL USE) to support roofing systems.

Greek Architecture and American Buildings

Architectural Terms

Architectural Terms and Definitions

File:Under-purlins.png - Wikipedia, the free encyclopedia

File:Cee-portal.jpg - Wikipedia, the free encyclopedia

THIS is what you are thinking of: (in Figure 26.37)
Architectural Drafting & Design - Google Books

JP: Chill, will you? I have as many of those references as you. If you read my post, you will see that I am not disagreeing with the formal definition, rather with the way the term is actually used in the real world (assuming that you regard Texas in that particular way).

Webster's goes so far as saying a purlin is any horizontal roofing member. Go figure.

The vast unwashed and misinformed also refer to meat and beans as "chili" (from the Spanish chile con carne - peppers with meat) in certain parts of the country. Every Texan knows there are no beans in chili. Yankess who eat chile con frijoles (peppers with beans) are quite full of S#it.

got to agree with jerry here

Originally Posted by brian schmitt

got to agree with jerry here

BS: Just how much is JP paying you anyhow?

Originally Posted by A.D. Miller

JP: Chill, will you? I have as many of those references as you. If you read my post,

Aaron,

If you read my post ...

You will see that I was replying to:

Originally Posted by Michael Garrity

Purlins in relation to roof structure mean only one thing.Support for the rafter

Must be a regional thing. Up here we refer to purlin as a strip of wood mounted perpendicular to the rafter (on top). Commonly 1x2 I believe.

Purlins are horizontal roofing members. The rafter supports are correctly called "under-purlins".
Ray, you started it, should have said "strapping".

Soffit venting is optional in a 1920's house, unless the attic has been super-insulated, then it needs full venting.

A purlin can be used on residential and commercial construction.It is a structural support for the rafters.Nothing else.We can all learn something everyday.After 38 years in construction on 2 continents and 5 countries I am still learning.Construction methods and materials are changing all the time.The inspector who knows "everything" is a poor inspector.Continuing education is the key.Everyone have a great day.

Originally Posted by John Kogel

Purlins are horizontal roofing members. The rafter supports are correctly called "under-purlins".
Ray, you started it, should have said "strapping".

Soffit venting is optional in a 1920's house, unless the attic has been super-insulated, then it needs full venting.

Is there a code requiring "soffit" vents?

Originally Posted by Vern Heiler

Is there a code requiring "soffit" vents?

VH: As, in the Flahidian's astute opinion, they could possibly be loosely construed as horizontal roof members, you may be asking about "purlin vents". But then, like RW said, it is a regional thing.

Aaron, I view the discussions over terminology as friendly banter to fill slow times. There are a half cozen terms to describe the same component for most of the parts used to makeup a structure, sometimes regional but most times recognizable within its context. I don’t care what you call it as long as I understand what it is.

John K. indicated that soffit vents are required for all attic venting sometime after 1920. I don’t know of a code requiring “soffit vents”. John also refers to “Full venting”. What is “Full venting”?

What is “Full venting”?

VH: It is what I do most of the time.

Originally Posted by Vern Heiler

Aaron, I view the discussions over terminology as friendly banter to fill slow times. There are a half cozen terms to describe the same component for most of the parts used to makeup a structure, sometimes regional but most times recognizable within its context. I don’t care what you call it as long as I understand what it is.

John K. indicated that soffit vents are required for all attic venting sometime after 1920. I don’t know of a code requiring “soffit vents”. John also refers to “Full venting”. What is “Full venting”?

Sorry Vern, I said nothing about requirements, and made no mention of code. It is good practice to add soffit vents if adding attic insulation in my area.

Originally Posted by Michael Garrity

A purlin can be used on residential and commercial construction.It is a structural support for the rafters.Nothing else.We can all learn something everyday.After 38 years in construction on 2 continents and 5 countries I am still learning.Construction methods and materials are changing all the time.The inspector who knows "everything" is a poor inspector.Continuing education is the key.Everyone have a great day.

"It is a structural support for the rafters.Nothing else."

As I stated above, incorrect.

"We can all learn something everyday."

Only if our minds are open to doing so. Saying it is not the same as doing it. Your mind apparently is closed to learning.

Quote:

Originally Posted by Jerry Peck
Incorrect as current construction methods are.

Purlins were laid across beam to support rafters which were installed on top of the purlins - the purlins spanned from beam to beam.

Today purlins are used for two uses:
1) under rafters to support the rafters and reduce their effective span
2) across the top of rafter trusses (which, by the way, is THE ORIGINAL USE) to support roofing systems.

Greek Architecture and American Buildings

Architectural Terms

Architectural Terms and Definitions

File:Under-purlins.png - Wikipedia, the free encyclopedia

File:Cee-portal.jpg - Wikipedia, the free encyclopedia

THIS is what you are thinking of: (in Figure 26.37)
Architectural Drafting & Design - Google Books
Jerry
What is your definition of a rafter truss?
I am surprised at your choice of reading material

The term "purlin" is not a common word and many construction glossarys do not address it.
However, as I've been in construction longer than anyone on this board (I think?) and at least as the left coast of our country goes, "purlin" has always meant a strucural framing member installed to help support roof rafters usually mid-span between the ridge and outside wall plate thereby reducing their unsupported span. In other parts of the country the term may mean something else. In Mongolia, well I better not say what it means there.
California B-1 General Contractors license # 163019.

Originally Posted by Michael Garrity

Jerry
What is your definition of a rafters/truss?
I am surprised at your choice of reading material

The red text I added above is the same as the red text I added to my post to correct the typo.

Everywhere I've been (all over Florida) purlins are one of two things - as I described.

The "choice of reading material" was simply to show you the uses for the term "purlins" in pictorial form.

If you cannot make sense out of those, try "Metal Buildings 101": Kirby Building Systems - For Metal Building System Builders Only

Originally Posted by Jerry McCarthy

The term "purlin" is not a common word and many construction glossarys do not address it.
However, as I've been in construction longer than anyone on this board (I think?) and at least as the left coast of our country goes, "purlin" has always meant a strucural framing member installed to help support roof rafters usually mid-span between the ridge and outside wall plate thereby reducing their unsupported span. In other parts of the country the term may mean something else. In Mongolia, well I better not say what it means there.
California B-1 General Contractors license # 163019.

JM: Thank you.

"Thank you."

Dang, Aaron
Two, nice post, IN ONE DAY.
Are you OK?

Originally Posted by Rick Cantrell

"Thank you."

Dang, Aaron
Two, nice post, IN ONE DAY.
Are you OK?

.
......
.

Dang, Aaron
Two, nice post, IN ONE DAY.
Are you OK?

RC: I've reformed.

Originally Posted by Billy Stephens

.
......
.

??????

Truss Roof - Purlin - Purcell Timber Frames, Nelson BC Canada

Originally Posted by Raymond Wand

Truss Roof - Purlin - Purcell Timber Frames, Nelson BC Canada

Raymond,

Yep, same thing I've been showing them ... some just do not want to read or listen, huh?

Mark,lots of fun on this thread.Was your question answered?Most posters are nice and informative but a select few just like to be nasty.Give me a call sometime.

Michael

Don't be dissuaded. Keep posting. I am not always right either and I am wrong sometimes just as much as the others!

Cheers,

Originally Posted by Michael Garrity

Most posters are nice and informative but a select few just like to be nasty.

And a select few just like to be obstinate and not read what is posted for the information and learning of all.

Some even state "We can all learn something everyday." and then refuse to read what is presented, instead making derogatory remarks about what is presented, and when a MANUFACTURERS information is present they then try to brush it off as others are the problem.

(sigh)

Oh well.

a select few just like to be obstinate and not read what is posted for the information and learning of all.

JP: I resemble that remark.

Thanks men for all your help, this forum, is like construction it's not a project if there's never a problem. Thanks again