Thomas Jefferson Papers

Notes and Drawings re Sheet Iron for Ridges and Gutters, 30 September 1804

Sep. 1804

to cover with sheet iron in ridges & gutturs

let the ridges be 6. I. high & 5. times that in span=30 I.

then the slope will be 16.15 and adding 1.85 I. for the lap the sheets of iron must be 18. I. wide

consequently 18 I. of sheet clears only 15. I. horizontal, and if the sheets cost 18. D. the square, the cost of a horizontal square will be as 15 I.:18 I.::18 D.:21.6 D

(note the thickest tin is 18. D a box of 100. sheets 16¾ by 12¼=142. sq. feet the thin tin is 18 D a box of 225 sheets 14 I. by 10 I.=220. sq. feet.)

method of doing it.

place your joists 30. I. apart from center to center. let them be 12. I. wide and slope them from the middle towards each end to 6. I. width, leaving the bolts in strait.

 laths are then to be nailed across them, but not plain ones as for shingling but serrated thus [GRAPHIC IN MANUSCRIPT] each tooth being of 30. I. long & 6. I. high, the thin point laid over the joist & nailed thro’ to the joist with a spike or large nail. to make the serrated laths without waste, have [out] plank 2. I. thick and 10. I. wide & split it with a saw thus


 in this way each plank makes 2 serrated laths without waste. nail them on the joists, the serrated edge up.

 then nail inch sheeting plank across them on the upper edges. the coat will consequently be parallel with the joists.

the angle of the tooth being 136.° 22’ have all your sheets bent longitudinally through the middle to that angle.

lay down a sheet in the guttur, and nail it’s edges to the sheeting. they will reach 9 I. up the slope each way.

lay another sheet on the adjoining ridge. it’s edge will overlap the guttur sheet 1.85 I. nail it on it’s ridge pole to the sheeting. note the sheeting is not to be mitred at the ridge pole, but the side of one plank laid over the edge of the other, that the nails may enter the solid, instead of entering the mitre.

then across the ridges, (after all is covered with sheet iron) lay plain laths one foot apart. these will consequently be parallel with the serrated lathes and across these again nail flooring planks, square jointed, which of course will be parallel with the joists & sheeting plank. the whole looks thus


[GRAPHIC IN MANUSCRIPT] a plinth to cover the eve-holes. a nail thro’ the flooring plank into the edge of the plinth another thro’ the plinth into the edge of the lath

estimate for every 10. f. square horizontal measure.

sheet iron. 120 sq. feet=21.60 D
flooring plank. 100. f.
laths 50.
sheeting 120.
270. sq. f. I. plank= 3.60
2. I. serrated laths oak 10 sq f.  .40
25.60 besides nails & laying down.

The Terras on the top of the house is 12. squares. will cost 307.20
The Terras on the N.W. offices. 30. squares } 38. sq 972. 
on the passage  8
do. on S.E. side 972. 

for the Terras of the house, of sheets 18. I. by 10. f. 48x2= 96.
for the 8. gutturs of the porticos & piazzas 20
for the gutturs formed by junction of the roof with walls of Dome  3

but if plate iron be used only for the gutturs, it may be only 16. I. wide and 11 f. 6. I. long

the ridges to be covered either with plank or shingles 12. I.

then the cost of the sheet iron will be only 8. D. per square horizontl. measure qu. 9. D 60

one Terras & passage will then cost 304. D. for it’s gutturs of sheet iron.

the terras, without the passage, 30. squares @ 9.6 will be 288. D for the sheet iron=16 squares @ 18. D

the ridges all s[h]all be 30. I. span & 6. I. high, & the slope 16.15

order 1500. F. plank pine 8. I wide in cuts of 10. f. for slopes of terras.

a plainer calculation

there being 4. gutturs in every 10. f. requiring only a sheet of 16. I. each & the full square of sheet iron costing 18. D. we have this proportion

As 10. f.: 4x16 I=5f-4 I::18 D: 9.6 D which xd. by 30. squares
gives 288. D. for the N.W. offices
& 288  for the S.E. do.
576.  for the whole
to wit 16. squares for N.W.
16. do  S.E.
32 do. for the whole x 18=576.

1804. Sep. 4. the N.W. office will require 2x48=96 sheets 16. I. wide 11 f-6 I long
wrote to Jones & Howell for 100. sheets 16. I. wide 11 f-8. I long
these will make 15.56 square which @ 18. D. will be 280. D.
Sep. 5. 06. wrote to Saml. Mifflin for 100. sheets 16 I. wide 11. f. 8 I. long.
May. 25. 07. wrote to Jones & Howell for 200. sheets 16. I. wide & 6. f. long, and 2. sheets of milled lead of 4. or 5. ℔ to the foot.

MHi: Coolidge Collection.

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