I do not believe that what started the fire is stated specifically, but it is significant that the house that burned down had a shingle roof, unlike the tin roofs that are used now. Shingle is more natural, and has more beauty and character, while tin is cold; shingle, however, is more vulnerable to destruction, it burns, while tin does not. I think that the roofs might be a metaphor for Black heritage, and what it means to truly appreciate it, according to the author.
Maggie was burned and scarred in the fire. Her mother remembers carrying her away "with her hair smoking and her dress falling off her in little peppery flakes", while Dee stood apart, watching the house burn from "under the sweet gum tree". Maggie was always the one who lived her heritage in the simple things of everyday, while Dee never touched its richness, looking upon it with scorn.
Dee wants only to escape her past, denying the good along with the bad of the Black experience. She thinks that she can keep her heritage alive through artifacts. Her concept of her rich African American roots is sterile, like the tin roofs on the houses. Maggie, on the other hand, has captured the spirit of her culture. Even though, like the shingle roof, its outward manifestations are subject to destruction, its essence lives on in people like Maggie, who are not afraid to proclaim their heritage through "everyday use".