President Donald Trump is expected to propose an initial $5.9bn (£4.56bn). Texas authorities say the state might need more than $125bn.
At least 39 people have died in the storm and its aftermath. East of Houston, floodwaters are still rising.
Visiting Texas, Vice-President Mike Pence promised federal help to "rebuild bigger and better than ever before".
Houston floods: White House seeks disaster aid from Congress - BBC NewsThe White House also said Mr Trump would donate $1m of his own money to the relief effort.
I am a pretty vocal opponent to many of the presidents current initiatives. But I am happy to see him take a step to help, personally. While I did his rally style visit to Texas strange, credit where credit is due.