[time-nuts] frying pan antenna

Joseph M Gwinn gwinn at raytheon.com
Tue Mar 16 23:55:41 UTC 2010


time-nuts-bounces at febo.com wrote on 03/16/2010 02:44:49 PM:

> From:
> 
> Chuck Harris <cfharris at erols.com>
> 
> To:
> 
> Discussion of precise time and frequency measurement 
<time-nuts at febo.com>
> 
> Date:
> 
> 03/16/2010 03:17 PM
> 
> Subject:
> 
> Re: [time-nuts] frying pan antenna
> 
> Sent by:
> 
> time-nuts-bounces at febo.com
> 
> Joseph M Gwinn wrote:
> > The tar paper is there primarily to reduce air infiltration when the 
wind 
> > blows.  Now days this purpose is served by the white housewrap, the 
> > original brand being Tyvek. 
> 
> That doesn't follow.  Most houses in the US have attics below 
> the shingles that are open to free air by way of soffit vents.

Ahh.  I was talking about the side walls, not the roof.  We do lots of 
wood shingles and clapboard on walls here in New England, but the roofs 
are usually asphalt shingles.

 
> Even in the case of cathedral ceilings, the space below the 
> roof sheathing is open to the outside air... to not do so will seriously 

> compromise the shingle life due to excess heating.

In the summer, and cause ice dams in the winter.

I gather from your email provider that you are in the Washington, DC area, 
where summers are far more brutal than up here in the frozen north.  (I 
used to live in Washington and Baltimore.)

 
> Tyvek is never used on roofs.  It is always too slippery for walking on.

True.


> > Water that blows past the shingles is stopped by the tarpaper or 
> > housewrap, keeping the sheathing and insulation dry.
> 
> Nope.

Side wall versus roof.


> There are two layers of shingles over any given part of the roof. Modern
> asphalt shingles have an asphalt glue down strip that ties the shingle
> tabs to the course below.  There isn't going to be any air infiltration
> of significance.

I don't know how true that will be after a few years, but the overlap 
keeps the water out, unless there is an ice dam.

 
> Builders and roofers are of a mixed mind over tarpaper.  Many leave it
> off because it is a hazard to the roofers.  The stuff is very slippery
> if it gets even the slightest bit wet.
> 
> The roof stays dry either way.

Here in New England, ice dams are the big issue, and lots of people have 
an EPDM rubber sheet put down between sheathing and roof shingles for this 
reason.  Heavy tarpaper or tarred felt was supposed to perform this 
function as well, but as you say its effectiveness was always debated, 
especially after it had dried out and cracked.  The rubber is supposed to 
last 50 years, though.


Joe Gwinn

 
> -Chuck Harris
> 
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