technology and the time period that allows this to be built. [inaudible]? could you describe why cast iron [inaudible]?has >> i think walter's intent was looked like masonry. be idn't intend for this to a modern structure. he intended it to be appropriate to the rest of the capitol design. but, because of weight it could not have been built in masonry. just finished several years earlier the liberal of in the renovation capitol where once it will been destroyed by fire he went in interior roof structure which was made of very elaborate cast iron. that, he proved the resi resilience and economy of cast make multiple can hadn't pieces from a single mold and was able to then create this dome without an extensive cost lightweight gh possible.at it was [inaudible]? the existing foundations wouldn't support a structure so was calculated to what it would have been. say it would have been considerably higher than the 14 million pounds that the decisions were hat was element ultimately -- ultimately built. the walls that you are leaning original ball fin the ll finch drum for original capitol. so everything he added was above the cornice level at this eventually. this before been originally exposed to view from the east and west front. you can see overhead how the brackets extend out to pick up columns of this past the columns are drainage columns and other half of ventilation columns. odd to have been very leave that cantilevered ondition exposed to view so he created a skirt of iron work transition from to captantilevered skirt out the rest of the capitol. you can see the great condition to achieve able with the restoration at this poi point. completely s been restor restored. ead business paints were abated. aar and new was repaired paint installed. n addition we cleaned and conserve and repainted the stone walls tpeufrpfinch and this ring of masonry that is is the et thick that foundation for the iron work that extends above. brackets, we only see eight feet of them now. an additional seven feet embedded in the masonry work and that acts as a huge supports the t weight of the tkoefpl and transfers it -- dome and evenly on to the stone walls below. here you get a good sense for cantilever beyond of the bull walls alternating d how columns are used for drainage provide nd others just passive ventilation. on my right, your left, you see some en it was installed of the chimneys of the capitol were captured within that used the hollow columns as a way to get that -- smoke ust out exhaust out. i have seen a couple of hotographs where he had the smoke billowing out at the oilerplate level and it is the chimney smoke that is coming out. ou can begin to really appreciate the beauty of the rotunda and the accomplishment adding this additional height to the space. the actual interior dome is not much larger than what bull finch would have had but his would have rested on the stone below where you see a of ecting cornice and band stone just above it. that is where the original dome would have sprung. so, we are now almost at the domeof where the bullfinch ould have ended and walters lifted that on additional drums to give height and light into rotunda. he here, everything above the sand is what was added as part ' addition. from the top of the sand stone balance laws trade -- predominantly s masonry with some cast iron elements. c offers are cast iron and the cornice below that area is cast iron but everything else is coating.ith a plaster >> we are about -- we are in the ange of i would say close to 100 feet. at this level you can appreciate frieze and what was space.ned for the he didn't start painting it ntil 1870 and managed to get about three-quarters of the way 1880.d before his death in complete isioned to the entire work but his early him from luded finishing it. bk was picked up based on it sketches and carried forward to the california gold ru rush. once you get to the california rush his work ends and alan ox's work continues to include of civil war and the birth flight, which then takes us back o the discovery of america by christopher columbus. as you look across the rotunda, ou can see evidence of some water leaks that have occurred over time. the lowest g below band of ornamentation on the dome, some of the stepping, you will see evidence the balustrade below past water intrusions. tears of gasltiple jets one before the cornice where you see light fixtures. base of the balustrade work where you see remnants of an earlier lighting scheme, the conduit with sockets. there was a string of lights at cup -- coupola over 1,000 gas lluminate with i will the quick of a switch from a battery in the lower level of the capital. can imagine at night it must have been quite a dramatic effect to see this all once.inate at of course, as electricity was introduced to the building in turn of the 20th century those goes fixtures were electrical h lighting and now we are using a more modern system to illuminate rotunda. the engineers for the project had all of the lower evel pieces stamped with his name. so you look at some of the nuts that.lts it will say for it?he take credit >> i'm sure you heard about the controversy between two eagle questions, walter i altering being a great architect and meigs a phenomenal engineer. have credit o both for creating the dome and without either of them it couldn't have happened but it merging of their talents that allowed it to come into being. building to erfect deal with egos. >> exactly. this.e show you we are passing through the boilerplate plenum.late we are at the top of the balcony that we don't open to the public because it is fairly large and on. to control groups but it does offer us an pportunity to really show you graphically how thin the cast ron shell of the dome really is. coffer which his .ou can see the exterior and interior that you can see from the rotunda floor. ironically, this is also how you would get outside to change the that cornice. on more thanksthat any to modern lighting technology we don't get out there. is always impressive to me to look through this thin layer and see for the first time just how the dome is constructed. let me know when you are done and i will close it. heavy is that? >> very. and it is supported mostly by the hinge. lifting it a little. please be very careful as you come through the next run of stairs. is a window that sets into you needcase a bit and to watch your shoulder. you can also begin to appreciate here the structure and design of dome. trusses, 363 s rib total, that create -- 36 in con thiical and a then it pecks up the exterior skin. the interior shell is not and aligning with the super structure that is from it and the exterior shell is projecting beyond it. keep in mind when the dome was finished this wall would not here.een this wall and windows were added in the 1940's when air introduced into the capitol. so, that is why you have the railing on the interior side. does this er why balcony need two railings. view on have had the the back side that would have allowed,more light to come this balcony level. we are a considerable distance apart. you should be able to hear me pretty clearly. is an amazing space. you have to be very careful what up are saying when you are here because anyone on the often sit side can hear you. >> [inaudible]? > 12 of these windows will be removed. if you look above the pavilion that we entered through there is that extends out. during an earlier phase we left usedbracket in place to be as a lifting hoist for the other lifted ets that will be to this area. so the 12 brackets will extend a over this railing and netting system will be suspended over the rotunda. of that netting is twofold. it provides protection to the rotunda can he remain open while we do our work. decorative has a drapery on the under side so it looks appropriate for the for ceremonial events that could occur or for the visitors visiting the capitol. at the present time to safety e an industrial netting. >> [inaudible]? it we er than replacing will be repairing it with an system much like you would repair a windshield on your car if you had a crack. use a heat and vacuum to it with a binder that seals the joint. our goal is to preserve as much as he original material possible. that is why the lock and stitch technique that we are using to the original pieces back together is so important to our because we. fforts to save as much of the historic artifact as we can. are there any examples of the lock and stitch? >> unfortunately all of them of the skirt art project have been overpainted. that is the beauty is you don't they are complete. but notice that we're now over and there is a tin canopy on top acting as an umbrella to ensure if there is a leak in the exterior skin it is caught and drained away so it leak in the exterior skin it is caught and drained away so it doesn't affect the painting. now we are at the tallest level. go out it door. please be careful when you go through this doorway t. is very low. be very mindful that the iron is very hard and 9 last thing you your head on hit this. so, please be very careful and go through the doorway. radial scheme he and how the capitol is the focal oint of washington is so clear at this point. the access of the mall, maryland avenue, pennsylvania avenue, all radiating from this central poi point. ust the beauty of the city opens before you when you stand at this level. top plate at the there are a series of through railing t hold the together. ballusters. ugh the as rust has developed and the the top s pushed up plate has cracked and that is stress in the iron work. what it does is compromise the structural integrity of that piece.lar we are not concerned about it because there is so much edundancy in the iron work design but we put it here as a measure to ensure that until work is repaired during this phase we don't have any forces against the railing. he me it is symbolic of t joining of both parties in to come together to fund an effort that is to our ly important count country. preserve being the capitol dome preserving the capitol dome is not a question for discussion. it is something that has to happen. is no more recognizable symbol of the country than the capitol dome or our national flag. >> like raising the debt ceiling. exactly. i won't go there. example of r good the thinness of the shell. if you can get an image of this, the nk it tells people how structure works, the exterior and cast e dome ironworks. >> if you put your hand there it give as you sense of that. i can tell you that i removed 180,000 pounds of lead based our from the attic during first phase so i know it the dn't weigh more than amount of lead paint already taken off. just as when you came out watch head when you come through doorway.rway. there doorwa doorwayi doorways . >> that is the light that is on when the congress is in session, the convene light. it is four bulbs. another interstitial ace that is a hollow cavity below the statue base then the statue above that. s you see, no person is permitted above this platform under any circumstances. ust make sure there is someone in front of you. if there is somebody you can focus on it is easier. going down?re we here. will stop one of the things i wanted to point out to you here coming steps you will see that form theb trusses that super structure converge here to up to support the statue of freedom. as you can imagine, trying to 36 items into such a small pace at the top was too great so every third truss is the one that continues forward and the that flank it merge into its side for buttressing support. what you also see is the enormous super structure has bands that reach down to suspend the shell below. and it has a very thin element that reaches out to the shape of exterior dome. the brilliant thing about this dome is that the exposed to very harsh conditions in theoutside, very cold winter, extremely hot in the summer under direct sun. plates may approach 130 degrees fahrenheit. ut because they are held away from the super structure that heat dissipates in the iron work before it gets to the super structure so the relationship trusses see very little temperature swing during the which helps to maintain the structural integrity of the dome. does not move that much. but a lot of the damage that we he shells sing is in t nd they are exposed to wide temperature spinks, a lot of bush expansion and when the rust between the plates in binds the plates from moving and thetes enormous pressure in iron work which relieves itself by cracking. work in this stage will be addressing cracks in the exterior shell. as a huge erect or pieces come nteresting a foundry they had to mark each pace so they knew at what level of the dome each was to go so don't be surprised if you see these marks on every piece as you go down. clear pattern made and it was important it go in at they used the and marks to make sure the installers knew where to place it. remember in the opening talked about the cracked iial that had and had to be removed. you will notice there are a series of bolts that go through plate above the octagonal window there. ornamental piece that crests that window that. acorn finial is from. >> [inaudible]? >> the crack? [inaudible]. >> all of that will be preserved. our goal is to keep as much of fabric as possible. >> [inaudible]? be repaired, yes. >> there will be 12 of these the rotunda nto that support the netting system hat is suspended above the floor. >> from the render iing you couldn't tell. or plastic? that multilayered netting is meant to capture a load of pounds and more and so we tart with a very large net and layer of slightly smaller a very tight net to catch any small objects. all of that is concealed by a rive skrim that creates the image of the canopy that you saw in the briefing. >> a very tight net to is there shake something loose? >> if a nut were to fall or if there was a broken piece of iron. we want to belt and suspenders safety to protect the public and there is ample construction barriers there to reclude anything from happening. not that we are expecting it to appen but we want to ensure that it doesn't. everything, the bracket, the columns and the super structure was d the skin politics created in a foundry in cool and hunt.d once pool and hunt had finished he balcony up to t from that point forward all of he work was done by james fowler kirkland out of new york. the wires are part of a defunct bird proofing system. we will remove them and install passive netting system to keep smaller birds from nesting. started this project, inre was a major water event the fall of 1990 that deposited amount of worth r water on the floor of the row tunnel did. your -- row h tunnel did. it is through your investigations that we bird nesting materials and eating on the dome is what clogged